The separation characteristics and the pressure drop for deep bed filtration of heavy oil/water emulsion were experimentally investigated with granular beds of glass beads and Toyoura sand. A mathematical model for calculating the separation process was proposed on the basis of deep bed filtration theory. The filter coefficient was correlated by empirical formulas with particle diameter, particle shape factor and superficial velocity. Furthermore, a calculation model was presented for estimating the pressure drop and the hydraulic pressure distribution in granular beds by considering the deposition change of oil droplets in the pores calculated by both the deep bed filtration theory and the Kozeny-Carman equation. It was shown that the proposed method was useful for predicting the separation efficiency of oil droplets and the pressure drop for the separation of oil/water emulsion by granular beds.