Abstract: By combining Monte Carlo simulation with residual thrust and Sarma method, the reliability of slope under the random earthquake effect was studied. In the case of a slope in Three Gorges Reservior area, calculation results show that the safety factor with the random earthquake has close relation with the seismic acceleration; vertical seismic acceleration has less effect on the stability of slope when it is less than two thirds of that of horizontal seismic acceleration, and has notable effect when it is more than that of the horizontal seismic acceleration. It is clear that the influence of the earthquake is notable.