The equation for lidar return power is considered, in a small-angle approximation, with the allowance for the dependence of multiple scattering contribution on the disperse medium composition. The ratio between the multiply and singly scattered components of radiation is numerically studied for different optical thickness of a layer depending on the receiver field of view. The applicability of the diffraction approximation for the small-angle part of scattering phase function is estimated when describing lidar returns with the allowance for multiple scattering.