Aiming at the bottleneck problems of laser applications in the sea battle, the characteristics of laser diffusion from sea surface is studied with the method of Kirchhoff Approach. The more accurate backscattering coefficient and bistatic scattering coefficient are derived by analyzing and computing the laser scattering field from the rough sea surface and by modifying the shadowing effect in the process of computation using shadowing function. Finally, the relationship between the roughness of sea surface, incident angle and the laser diffusion reflectivity is obtained and some results can be taken as the theoretical basis for other relevant studies.