Spatially resolved reflection close to light source has drawn great attention in the fied of medical optics and photonics recently. This research is considered to develop a new noninvasive technique of measuring the optical properties of intravital biological tissue. It is limited to study the spatially resolved diffuse reflection of tissue close to light source with diffusion approximation. The radiance distribution close to light source can be analyzed by P3 approximation theory considering the third-order moment of phase function. The spatially resolved diffuse reflection based on P3 approximation is studied. The equation set of the P3 approximation and its Green function approximate solution are derived from the PN equation set of the transport theory. The relationship between P1 approximation and the diffusion approximation is demonstrated, and a complete solution of P3 approximation with the extrapolated boundary conditions and collimated beam approximation is obtained. The effects of the second-order parameter on the P3 approximation diffuse reflection are studied, and the results are compared with them of diffusion approximation and Monte Carlo simulation. The application range of P3 approximation is presented.