Abstract: With the hypothes is of parallel plate model for local aperture regions,the apertures are generat ed by using the statistical methods according to a certain aperture distribution,and the numerical simulations are performed for saturated seepage flow and unsaturated seepage flow in the fracture.The mechanism of both saturated seepage flow and unsaturated seepage flow is the difference of water pressure potential.For the unsaturated seepage flow,the pressure of wetting phase(water) is less than the pressure of nonwetting phase(air) everywhere in the field.The water flow is mainly in the large apertures for saturated seepage flow.On the contrary,the water flow is mainly in the little a pertures for unsaturated seepage flow.