The diffuse reflectance of single-fiber reflectance probe is studied with the Monte Carlo simulation, and we find that the sub-diffuse scattering light is sensitive to the scattering phase function (SPF) related to tissue microstructure. A semi-empirical diffuse reflection model for small aperture measurement is studied, and the influences of second-order and third-order optic parameters on this model are analyzed. It shows that the two parameters have contrary effects on diffuse reflectance, and both effects are non-negligible for optically anisotropic biological tissues. A simplified semi-empirical model and its application condition are given, which provides potentially applicable support for measurement of tissue scattering properties and associated microstructure.