Zhen Cao The LHAASO Collaboration, F. Aharonian The LHAASO Collaboration, Y. X. Bai The LHAASO Collaboration, Y. W. Bao The LHAASO Collaboration, D. Bastieri The LHAASO Collaboration, X. J. Bi The LHAASO Collaboration, Y. J. Bi The LHAASO Collaboration, W. Bian The LHAASO Collaboration, A. V. Bukevich The LHAASO Collaboration, C. M. Cai The LHAASO Collaboration, W. Y. Cao The LHAASO Collaboration, Zhe Cao The LHAASO Collaboration, J. Chang The LHAASO Collaboration, J. F. Chang The LHAASO Collaboration, A. M. Chen The LHAASO Collaboration, E. S. Chen The LHAASO Collaboration, H. X. Chen The LHAASO Collaboration, Liang Chen The LHAASO Collaboration, Long Chen The LHAASO Collaboration, M. J. Chen The LHAASO Collaboration, M. L. Chen The LHAASO Collaboration, Q. H. Chen The LHAASO Collaboration, S. Chen The LHAASO Collaboration, S. H. Chen The LHAASO Collaboration, S. Z. Chen The LHAASO Collaboration, T. L. Chen The LHAASO Collaboration, X. B. Chen The LHAASO Collaboration, X. J. Chen The LHAASO Collaboration, Y. Chen The LHAASO Collaboration, N. Cheng The LHAASO Collaboration, Y. D. Cheng The LHAASO Collaboration, M. C. Chu The LHAASO Collaboration, M. Y. Cui The LHAASO Collaboration, S. W. Cui The LHAASO Collaboration, X. H. Cui The LHAASO Collaboration, Y. D. Cui The LHAASO Collaboration, B. Z. Dai The LHAASO Collaboration, H. L. Dai The LHAASO Collaboration, Z. G. Dai The LHAASO Collaboration, Danzengluobu The LHAASO Collaboration, Y. X. Diao The LHAASO Collaboration, X. Q. Dong The LHAASO Collaboration, K. K. Duan The LHAASO Collaboration, J. H. Fan The LHAASO Collaboration, Y. Z. Fan The LHAASO Collaboration, J. Fang The LHAASO Collaboration, J. H. Fang The LHAASO Collaboration, K. Fang The LHAASO Collaboration, C. F. Feng The LHAASO Collaboration, H. Feng The LHAASO Collaboration, L. Feng The LHAASO Collaboration, S. H. Feng The LHAASO Collaboration, X. T. Feng The LHAASO Collaboration, Y. Feng The LHAASO Collaboration, Y. L. Feng The LHAASO Collaboration, S. Gabici The LHAASO Collaboration, B. Gao The LHAASO Collaboration, C. D. Gao The LHAASO Collaboration, Q. Gao The LHAASO Collaboration, W. Gao The LHAASO Collaboration, W. K. Gao The LHAASO Collaboration, M. M. Ge The LHAASO Collaboration, T. T. Ge The LHAASO Collaboration, L. S. Geng The LHAASO Collaboration, G. Giacinti The LHAASO Collaboration, G. H. Gong The LHAASO Collaboration, Q. B. Gou The LHAASO Collaboration, M. H. Gu The LHAASO Collaboration, F. L. Guo The LHAASO Collaboration, J. Guo The LHAASO Collaboration, X. L. Guo The LHAASO Collaboration, Y. Q. Guo The LHAASO Collaboration, Y. Y. Guo The LHAASO Collaboration, Y. A. Han The LHAASO Collaboration, O. A. Hannuksela The LHAASO Collaboration, M. Hasan The LHAASO Collaboration, H. H. He The LHAASO Collaboration, H. N. He The LHAASO Collaboration, J. Y. He The LHAASO Collaboration, X. Y. He The LHAASO Collaboration, Y. He The LHAASO Collaboration, S. Hernández-Cadena The LHAASO Collaboration, Y. K. Hor The LHAASO Collaboration, B. W. Hou The LHAASO Collaboration, C. Hou The LHAASO Collaboration, X. Hou The LHAASO Collaboration, H. B. Hu The LHAASO Collaboration, S. C. Hu The LHAASO Collaboration, C. Huang The LHAASO Collaboration, D. H. Huang The LHAASO Collaboration, J. J. Huang The LHAASO Collaboration, T. Q. Huang The LHAASO Collaboration, W. J. Huang The LHAASO Collaboration, X. T. Huang The LHAASO Collaboration, X. Y. Huang The LHAASO Collaboration, Y. Huang The LHAASO Collaboration, Y. Y. Huang The LHAASO Collaboration, X. L. Ji The LHAASO Collaboration, H. Y. Jia The LHAASO Collaboration, K. Jia The LHAASO Collaboration, H. B. Jiang The LHAASO Collaboration, K. Jiang The LHAASO Collaboration, X. W. Jiang The LHAASO Collaboration, Z. J. Jiang The LHAASO Collaboration, M. Jin The LHAASO Collaboration, S. Kaci The LHAASO Collaboration, M. M. Kang The LHAASO Collaboration, I. Karpikov The LHAASO Collaboration, D. Khangulyan The LHAASO Collaboration, D. Kuleshov The LHAASO Collaboration, K. Kurinov The LHAASO Collaboration, B. B. Li The LHAASO Collaboration, Cheng Li The LHAASO Collaboration, Cong Li The LHAASO Collaboration, D. Li The LHAASO Collaboration, F. Li The LHAASO Collaboration, H. B. Li The LHAASO Collaboration, H. C. Li The LHAASO Collaboration, Jian Li The LHAASO Collaboration, Jie Li The LHAASO Collaboration, K. Li The LHAASO Collaboration, L. Li The LHAASO Collaboration, R. L. Li The LHAASO Collaboration, S. D. Li The LHAASO Collaboration, T. Y. Li The LHAASO Collaboration, W. L. Li The LHAASO Collaboration, X. R. Li The LHAASO Collaboration, Xin Li The LHAASO Collaboration, Y. Z. Li The LHAASO Collaboration, Zhe Li The LHAASO Collaboration, Zhuo Li The LHAASO Collaboration, E. W. Liang The LHAASO Collaboration, Y. F. Liang The LHAASO Collaboration, S. J. Lin The LHAASO Collaboration, B. Liu The LHAASO Collaboration, C. Liu The LHAASO Collaboration, D. Liu The LHAASO Collaboration, D. B. Liu The LHAASO Collaboration, H. Liu The LHAASO Collaboration, H. D. Liu The LHAASO Collaboration, J. Liu The LHAASO Collaboration, J. L. Liu The LHAASO Collaboration, J. R. Liu The LHAASO Collaboration, M. Y. Liu The LHAASO Collaboration, R. Y. Liu The LHAASO Collaboration, S. M. Liu The LHAASO Collaboration, W. Liu The LHAASO Collaboration, X. Liu The LHAASO Collaboration, Y. Liu The LHAASO Collaboration, Y. Liu The LHAASO Collaboration, Y. N. Liu The LHAASO Collaboration, Y. Q. Lou The LHAASO Collaboration, Q. Luo The LHAASO Collaboration, Y. Luo The LHAASO Collaboration, H. K. Lv The LHAASO Collaboration, B. Q. Ma The LHAASO Collaboration, L. L. Ma The LHAASO Collaboration, X. H. Ma The LHAASO Collaboration, J. R. Mao The LHAASO Collaboration, Z. Min The LHAASO Collaboration, W. Mitthumsiri The LHAASO Collaboration, G. B. Mou The LHAASO Collaboration, H. J. Mu The LHAASO Collaboration, Y. C. Nan The LHAASO Collaboration, A. Neronov The LHAASO Collaboration, K. C. Y. Ng The LHAASO Collaboration, M. Y. Ni The LHAASO Collaboration, L. Nie The LHAASO Collaboration, L. J. Ou The LHAASO Collaboration, P. Pattarakijwanich The LHAASO Collaboration, Z. Y. Pei The LHAASO Collaboration, J. C. Qi The LHAASO Collaboration, M. Y. Qi The LHAASO Collaboration, J. J. Qin The LHAASO Collaboration, A. Raza The LHAASO Collaboration, C. Y. Ren The LHAASO Collaboration, D. Ruffolo The LHAASO Collaboration, A. Sáiz The LHAASO Collaboration, M. Saeed The LHAASO Collaboration, D. Semikoz The LHAASO Collaboration, L. Shao The LHAASO Collaboration, O. Shchegolev The LHAASO Collaboration, Y. Z. Shen The LHAASO Collaboration, X. D. Sheng The LHAASO Collaboration, Z. D. Shi The LHAASO Collaboration, F. W. Shu The LHAASO Collaboration, H. C. Song The LHAASO Collaboration, Yu. V. Stenkin The LHAASO Collaboration, V. Stepanov The LHAASO Collaboration, Y. Su The LHAASO Collaboration, D. X. Sun The LHAASO Collaboration, H. Sun The LHAASO Collaboration, Q. N. Sun The LHAASO Collaboration, X. N. Sun The LHAASO Collaboration, Z. B. Sun The LHAASO Collaboration, N. H. Tabasam The LHAASO Collaboration, J. Takata The LHAASO Collaboration, P. H. T. Tam The LHAASO Collaboration, H. B. Tan The LHAASO Collaboration, Q. W. Tang The LHAASO Collaboration, R. Tang The LHAASO Collaboration, Z. B. Tang The LHAASO Collaboration, W. W. Tian The LHAASO Collaboration, C. N. Tong The LHAASO Collaboration, L. H. Wan The LHAASO Collaboration, C. Wang The LHAASO Collaboration, G. W. Wang The LHAASO Collaboration, H. G. Wang The LHAASO Collaboration, H. H. Wang The LHAASO Collaboration, J. C. Wang The LHAASO Collaboration, K. Wang The LHAASO Collaboration, Kai Wang The LHAASO Collaboration, Kai Wang The LHAASO Collaboration, L. P. Wang The LHAASO Collaboration, L. Y. Wang The LHAASO Collaboration, L. Y. Wang The LHAASO Collaboration, R. Wang The LHAASO Collaboration, W. Wang The LHAASO Collaboration, X. G. Wang The LHAASO Collaboration, X. J. Wang The LHAASO Collaboration, X. Y. Wang The LHAASO Collaboration, Y. Wang The LHAASO Collaboration, Y. D. Wang The LHAASO Collaboration, Z. H. Wang The LHAASO Collaboration, Z. X. Wang The LHAASO Collaboration, Zheng Wang The LHAASO Collaboration, D. M. Wei The LHAASO Collaboration, J. J. Wei The LHAASO Collaboration, Y. J. Wei The LHAASO Collaboration, T. Wen The LHAASO Collaboration, S. S. Weng The LHAASO Collaboration, C. Y. Wu The LHAASO Collaboration, H. R. Wu The LHAASO Collaboration, Q. W. Wu The LHAASO Collaboration, S. Wu The LHAASO Collaboration, X. F. Wu The LHAASO Collaboration, Y. S. Wu The LHAASO Collaboration, S. Q. Xi The LHAASO Collaboration, J. Xia The LHAASO Collaboration, J. J. Xia The LHAASO Collaboration, G. M. Xiang The LHAASO Collaboration, D. X. Xiao The LHAASO Collaboration, G. Xiao The LHAASO Collaboration, Y. L. Xin The LHAASO Collaboration, Y. Xing The LHAASO Collaboration, D. R. Xiong The LHAASO Collaboration, Z. Xiong The LHAASO Collaboration, D. L. Xu The LHAASO Collaboration, R. F. Xu The LHAASO Collaboration, R. X. Xu The LHAASO Collaboration, W. L. Xu The LHAASO Collaboration, L. Xue The LHAASO Collaboration, D. H. Yan The LHAASO Collaboration, J. Z. Yan The LHAASO Collaboration, T. Yan The LHAASO Collaboration, C. W. Yang The LHAASO Collaboration, C. Y. Yang The LHAASO Collaboration, F. F. Yang The LHAASO Collaboration, L. L. Yang The LHAASO Collaboration, M. J. Yang The LHAASO Collaboration, R. Z. Yang The LHAASO Collaboration, W. X. Yang The LHAASO Collaboration, Y. H. Yao The LHAASO Collaboration, Z. G. Yao The LHAASO Collaboration, X. A. Ye The LHAASO Collaboration, L. Q. Yin The LHAASO Collaboration, N. Yin The LHAASO Collaboration, X. H. You The LHAASO Collaboration, Z. Y. You The LHAASO Collaboration, Y. H. Yu The LHAASO Collaboration, Q. Yuan The LHAASO Collaboration, H. Yue The LHAASO Collaboration, H. D. Zeng The LHAASO Collaboration, T. X. Zeng The LHAASO Collaboration, W. Zeng The LHAASO Collaboration, M. Zha The LHAASO Collaboration, B. B. Zhang The LHAASO Collaboration, B. T. Zhang The LHAASO Collaboration, F. Zhang The LHAASO Collaboration, H. Zhang The LHAASO Collaboration, H. M. Zhang The LHAASO Collaboration, H. Y. Zhang The LHAASO Collaboration, J. L. Zhang The LHAASO Collaboration, Li Zhang The LHAASO Collaboration, P. F. Zhang The LHAASO Collaboration, P. P. Zhang The LHAASO Collaboration, R. Zhang The LHAASO Collaboration, S. R. Zhang The LHAASO Collaboration, S. S. Zhang The LHAASO Collaboration, W. Y. Zhang The LHAASO Collaboration, X. Zhang The LHAASO Collaboration, X. P. Zhang The LHAASO Collaboration, Yi Zhang The LHAASO Collaboration, Yong Zhang The LHAASO Collaboration, Z. P. Zhang The LHAASO Collaboration, J. Zhao The LHAASO Collaboration, L. Zhao The LHAASO Collaboration, L. Z. Zhao The LHAASO Collaboration, S. P. Zhao The LHAASO Collaboration, X. H. Zhao The LHAASO Collaboration, Z. H. Zhao The LHAASO Collaboration, F. Zheng The LHAASO Collaboration, W. J. Zhong The LHAASO Collaboration, B. Zhou The LHAASO Collaboration, H. Zhou The LHAASO Collaboration, J. N. Zhou The LHAASO Collaboration, M. Zhou The LHAASO Collaboration, P. Zhou The LHAASO Collaboration, R. Zhou The LHAASO Collaboration, X. X. Zhou The LHAASO Collaboration, X. X. Zhou The LHAASO Collaboration, B. Y. Zhu The LHAASO Collaboration, C. G. Zhu The LHAASO Collaboration, F. R. Zhu The LHAASO Collaboration, H. Zhu The LHAASO Collaboration, K. J. Zhu The LHAASO Collaboration, Y. C. Zou The LHAASO Collaboration, X. Zuo The LHAASO Collaboration

The core-collapse supernova remnant (SNR) Cassiopeia A (Cas A) is one of the brightest galactic radio sources with an angular radius of $\sim$ 2.5 $\arcmin$. Although no extension of this source has been detected in the $\gamma$-ray band, using more than 1000 days of LHAASO data above $\sim 0.8$ TeV, we find that its spectrum is significantly softer than those obtained with Imaging Air Cherenkov Telescopes (IACTs) and its flux near $\sim 1$ TeV is about two times higher. In combination with analyses of more than 16 years of \textit{Fermi}-LAT data covering $0.1 \, \mathrm{GeV} - 1 \, \mathrm{TeV}$, we find that the spectrum above 30 GeV deviates significantly from a single power-law, and is best described by a smoothly broken power-law with a spectral index of $1.90 \pm 0.15_\mathrm{stat}$ ($3.41 \pm 0.19_\mathrm{stat}$) below (above) a break energy of $0.63 \pm 0.21_\mathrm{stat} \, \mathrm{TeV}$. Given differences in the angular resolution of LHAASO-WCDA and IACTs, TeV $\gamma$-ray emission detected with LHAASO may have a significant contribution from regions surrounding the SNR illuminated by particles accelerated earlier, which, however, are treated as background by IACTs. Detailed modelling can be used to constrain acceleration processes of TeV particles in the early stage of SNR evolution.