Abstract: The discrete equivalent spherical scatterers aggregate model is developed for investigating the scattering characteristic of biological tissue. Combined with classic Mie theory, the phase function is calculated. The numerical results show that Mie phase function can not only describe the relationship between the equivalent diameter and the light intensity oscillation in backscattering region, which provides a theory tool of noninvasive or minimally invasive diagnosis and treat; but also interpret the dependency of scattering light intensity distribution on light wavelength, which supplies references to select incident light wavelength in practice. With proper parameters of particle size distribution, Mie phase function can characterize complex biological tissue.