A polydisperse sphere model with the complex refractive index is employed to describe the propagation of light in biological tissue.The scattering coefficient,absorption coefficient and scattering phase function are calculated.At the same time,the inverse problem on retrieving the particles size distribution,imaginary part of the refractive index and number density of scatterers is investigated.The result shows that the retrieval scheme together with the Chahine algorithm is effective in dealing with such an inverse problem.IT is also clarified that a group of parameters including the scattering coefficient,absorption coefficient and phase function are associated with another group including the refractive index,particle size distribution and number density of scatterers,which is a problem described in two different ways and the anisotropy factor is not an independent variable,but is determined by the phase function.