Zhirui Li, Hongrui Gu, Yongkang Sun, Yang Huang, Youjun Lu, Jifeng Liu

We simulate the optical searching of gravitational-wave electromagnetic counterpart of the binary neutron star (BNS) merger event (i.e., a kilonova) using the ground based {\it SiTian} project prototype telescope with a 5-min limiting magnitude of 22.0, triggered by LIGO and Virgo gravitational wave detectors during the ongoing O4 run. Our simulations show that an average of 0.17-0.25 kilonova events can be observed over the entire O4 period of $\sim 2$ years in the most optimistic case we set, while no kilonova can be detected in other cases. We note that it is beneficial for {\it SiTian}'s kilonova searching by extending the exposure time to gain deeper limiting magnitude despite the rapid decline of kilonova luminosity.