Multipath transmission of laser signal is caused by the optics scattering in undersea, and the received signal will be broadened in time domain. In this paper, the scattering characteristics of undersea wireless optical transmission were mainly analyzed, and Monte Carlo statistical method was used to simulate the time-domain broadening characteristics of laser signal in offshore seawater. Then the time domain broadening model of wireless optical transmission in offshore seawater of different pulse width optical signal was obtained. The results show that the time domain broadening of impulse signal in offshore area is increased rapidly with the increase of transmission distance and meets the Gauss distribution in a certain range, and the relationship between the transmission rate of optical signal and the transmission distance presents exponential decay.