The relationship between diffuse reflectance R measured close to the source and parameter γ related to collecting aperture , reduced scattering coefficient μ's,and scattering phase function is discussed. According to different biological tissues, different scattering phase functions are selected, and the diffuse reflectance data of photons passing through biological tissues are obtained by Monte Carlo simulation. The relationship between the reflectance R and dimensionless reduced scattering coefficient μ's , where is the collection aperture of scattered light, is validated by the data obtained. It is found that when μ's < 2, R is sensitive to the change of the scattering phase function and has a linear relation with μ's . The slope of R is a quadratic function with respect to γ. Results demonstrate that the diffuse reflectance R of the micro-area near the light source is sensitive to the change of γ. This provides a simple method for measuring γ related to the microstructure of biological tissues.