The transmittance and diffusivity are two key issues for light scattering materials but showing fairly sharp contradictions. A theoretical and computational model is derived to describe the volumetric diffusers based on multiple Mie scattering theory and Monte-Carlo methods. The scattering transmission processes of photons are simulated with statistic calculation to optimize the correlation between the optical performances and parameters, including relative refractive index, size, concentration of doped particles, geometrical structure of diffusers, and wavelength of the illumination source. It is found that, relative refractive index is the most sensitive parameter in above to get perfect diffusers, the optimized values are 0.91~0.97 or 1.03~1.09. The wavelength dispersion of transmittance and diffusivity can be fatherly eliminated and suppressed to meet the needs of practical applications.