A modified diffusion approximation is investigated. In this theoretical model, diffusion coefficient D of the standard diffusion approximation is substituted by diffusion coefficient Dasym of P3 approximation. Analytic solution RHybrid(ρ) of this hybrid diffusion for reflectance in single source approximation and steady-state case with extrapolated boundary is obtained; influences of the transport albedo a′ on the standard diffusion approximation RDA(ρ) and the hybrid diffusion approximation RHybrid(ρ) are compared; recovering of optical parameters from diffuse reflectance RHybrid(ρ) is demonstrated, and the errors and application ranges are studied. The results show that this hybrid diffusion approximation RHybrid(ρ) can be used in strong absorption media and at short source-detector separation.