Diffuse reflectance of tissue close to source about 1 transport mean free path (MFP) can be analyzed by P3 approximation theory, the light distribution of this area is dependent on scattering phase function of tissue. The influence of the structure factor (α) of the combined phase function on the diffuse reflectance light distribution close to source is studied in this paper. The research shows that when the transport MFP is kept constant, the light distribution close to source changes with the anisotropy factor g, but almost does not change in the region of the diffusion approximation; the influence of α on the diffuse reflectance is much more than the influence of the high-order moments of phase function on it. The research is very valuable for the in vivo measurement in endoscopic mode or in superficial tissue based on the spatial-resolved diffuse reflectance.