Steady-state diffuse reflectance based on P3 approximation is studied at short source-detector separations. In many practical applications, we can only measure the diffuse reflectance light close to the source, and attempt to derive the optical parameters of tissues from the collected data. In this paper, diffuse reflectance with different absorption coefficients and scattering coefficients at short source-detector separations is measured, and the experimental results are compared with that of P3 approximation. These studies show that P3 approximation can be used to describe the light contribution close to the source, and can be used to study strong absorption medium.