The model for transmembrane transport of suspended microparticles in microfiltration process has been developed. It describes transport of non-uniform suspension through heteroporous membrane and enables to calculate particle size distribution in concentrate and permeate. The model is based on the ＇＇sieve mechanism＇＇ using stochastic approach and permits to calculate the individual probability of penetration of fraction through pore with definite radius and overall probability of penetration of fraction with radius-rj through wide spectrum of pores. Diagonal array of individual probability has been built using developed algorithm is database for particle-size distribution in permeate and concentrate. The input data are the cumulative density function for suspension and probability density function for membrane. Particle size distribution in permeate and concentrate are calculated on the base of decomposition of particle-size distribution in feed suspension using probability density function for membrane pore-distribution. The model doesn＇t contain digital integration that makes it attractive by modelling sophisticated membrane-based hybrid processes.