A ray tracing model is used to deal with correlated scattering by denser dis-persoid. From the computation of phase function of each layer satisfying the condition of single scattering, the probability function of scat bering is obtained,which is then used to calculate the optical energy distribution by forward scattering. The optical energy distribution of multiple scattering is calculated by using iteration based on a proposed multiple scattering model however, for larger particles, the calculation may be based on the diffraction theory. In order to optimize under restrint the upper linit distribution function, the measured values of optical energy spectrum scattered by dispersoid sample of various densities are compared with those obtained by simulation. The optimizing result obtained is used to calculated D32. The experimental results are complred with the statistical data.