Earthquake ground motions have the characteristics of randomness and will lead to the stochastic behavior of high concrete face rockfill dam (CFRD) slopes; therefore, it is necessary to investigate the slope dynamic stability using stochastic analysis methods. A recently developed generalized probability density evolution method (GPDEM) coupling with spectral representation-random function method is presented to obtain the stochastic and evaluate the seismic reliability of dam slope stability based on the safety factor and the cumulative time of safety factor less than 1.0 (Fs<1.0) under stochastic seismic excitation. Comparison between the results of the Monte Carlo method (MCM) and GPDEM analysis demonstrates the effectiveness and high accuracy of the GPDEM. The reliability analysis of dam slopes can directly reflect the stability probability and degree of safety, indicating the novel approach to dam slope stability assessment from a stochastic viewpoint.