Abstract.A power law relation between the filtration coefficients of straining and flux through small pores based on percolation theory has been reported. It was a monodisperse particle filtration theory, while the actual colloidal suspension is polydisperse particles. In this study, a formula of particle size distribution for the effluent polydisperse particle in staining-dominate deep bed filtration (DBF) process is proposed based on preliminary results of the monodisperse filtration theory. In order to validate this formula, a numerical staining-dominate DBF model is established to obtain particle size distribution for the effluent polydisperse particle, using the parameters of experimental data set to configure the simulation conditions. The numerical simulation is consistent with the predicted results calculated from the formula. It's indicated that the formula applied for the prediction of particle size distribution for the effluent polydisperse particle in staining-dominate DBF process is relatively accurate and effective.