Abstract: According to the fractal dimension, the disturbed distance between upper and lower fracture surfaces and the ratio of area contact (the proportion of contact area to whole area of fracture) of fracture, the random Brown Function is used to generate a rough walled fracture with position dependent aperture. Based on the parallel plate approximation for suitably small cell in the fracture plane, the fracture is divided into many equally spaced cells and numerical simulations are done for the process of unsaturated seepage flow during drainage and imbibition. In the light of the simulated results of water saturation and unsaturated permeability under different capillary pressure, drainage and imbibition curves are obtained and relationships between unsaturated permeability and capillary pressure during drainage and imbibition are also presented. The qualitative comparison of simulated results and experimental results shows that the method proposed in this paper is feasible and reliable to determine the unsaturated hydraulic parameters of rock fracture.