Influence of the scattering phase function on the diffuse reflection of a micro-region close to the source was investigated by Monte Carlo simulations, and relationship between a semi-empirical model of diffuse reflection and the optical parameters related to the phase function was analyzed. Research shows that the scattered light of the micro-region close to the source is very sensitive to the scattering phase function, and the sensitivity will gradually weaken with increasing of collection aperture φ.When φ>1.8 mm, influence of the scattering phase function on the diffuse reflection is not obvious and relative change in reflectivity is less than 1%; when φ<1.8 mm, influence of the scattering phase function on the diffuse reflection can reach up to 15.2%. When the anisotropic factor g and the second-order optical parameter γ are used to characterize a single-particle scattering properties, the differences of scattering properties are reflected in the third-order parameter δ. The diffuse reflectance decreases with the increasing of δ and the influence of δ on the diffuse reflectance can reach 9%.