For spatial-resolved diffuse reflectance, the sensitivity expression to the reduced scattering parameter μs' is derived and numerically analyzed in the two-point-source delta-P1 approximation of transport theory, and the influences of the scattering parameter μs' on the delta-P1 approximation reflectance, hybrid diffuse approximation reflectance, and diffusion approximation reflectance are also compared. The results show that the optical properties of biological tissue can be better described by the delta-P1 approxiamate model in relatively high scattering and absorbing medium for a short souce-detector separation; the optimum probe spacing ρopt is obtained and approximately equal to 2.7-4 transport mean free path for the reduced albedo a'>0.83, at which a variable reduced scattering coefficient has the smallest effect on the measurement of optical absorption in the turbid medium and ρopt reduces with the scattering parameter μs' increasing. The study is of great significance for optimizing the probe geometry and measuring the optical parameters of biological tissues.