Based on a theoretical model for spatial diffusion reflection with two-point-source -P1 approximation to the radiative transport equation for a semi-infinite homogeneous turbid medium, the optical absorption coefficient a, reduced scattering coefficient ' s, and the second-order parameter of the medium are recovered from the measurement data of the reflectance by the nonlinear least squares method. The results show that the two-point-source -P1 approximation can give more satisfactory results for describing irradiance distribution close to source when the source-detector separation is larger than one transport mean free path. We can also obtain the anisotropy factor g according to the relationship between and ' s. This study is of great significance for the measurement of the optical properties of biological tissues and the application of diffuse reflectance spectroscopy technology.