The purpose of this study is to develop a quasi-three-dimensional slope stability model based on limit equilibrium method for overcoming the huge computational effort and taking realistic conditions into consideration. The rainfall infiltration and groundwater level variation were simulated by solving the Green-Ampt theory and the one-dimensional Boussinesq equation for sloping aquifer simultaneously. The three-dimensional system was divided into several two-dimensional layers. The stability of each layer was analyzed by using the simplified Bishop method. The three-dimensional stability condition with rainfall infiltration over time was therefore calculated by employing a weighted procedure where weighting was based upon arc-length or area of each layer. Under neglecting lateral flows, the effects of soil permeability, rainfall characters, rainfall patterns, inclined angle of rock layer, topography and soil properties on slope stability were discussed.