Proposed in this paper is an analyzing model for the slope reliability taking the random effects of the seepage field of groundwater and the dependent factors into consideration. Taking the Circle Slice Method as its base of mechanical analyses for the stability of a slope, the model can analyze the movement of groundwater by using BEM and calculate the slope reliability index, β ,and probability of failure, P, by means of Monte Carlo Method (FOSM). The way sampling on the failure surface adopted in the paper incorporates the strong points of Monte Carlo Method and First Order Second Moment Method, and its calculating efficiency is remarkably higher than that of traditional Monte Carlo Method. Employing the model proposed, the reliability indexes and probabilities of failure of a real slope are estimated. The tendencies and extents of influence of rainfall supply and the uncertainty of anisotropic character of media in permeability on the slope reliability are studied for the first time.