  Mergers of binary neutron stars are multimessenger sources of gravitational
waves that have an optical luminous counterpart, commonly referred to as
'kilonova'. Inspired by the detection of GW170817, intensive searches have been
conducted during the LIGO/Virgo O3 run. However, despite these efforts, no
verified kilonova was detected. In this work, we present a parameter constraint
method based on non-detection of optical searching considering both GW skymap,
limited sky coverage, cadence, limiting magnitudes and the probability of
astrophysical origin. We use our method to place constraints on EoS of neutron
star based on follow-up during O3 run and obtain $M_{\rm TOV} =
2.170^{+0.120}_{-0.108}\ M_{\odot}$ at 90\% confidence level with the
combination of other observations. And we also take outlook for WFST targeting
kilonova throughout the LIGO/Virgo O4 run. With more events handled, we will
obtain more stringent constraints on EoS and kilonova populations.
