Checking the dam's stability under seismic conditions has always been an important job for dam’s security; and using the reasonable calculation method is the basic guarantee for right result. The probability mean of reliability analysis for dam slope's stability is discussed based on the probabilistic limit analysis and the formulation what considered earthquake as a probability event for slope's reliability is deduced. To demonstrate the rationality of bringing exceeding probability into dam slope stability analysis

two typical examples and Xiaolangdi dam slope are taken to investigate the variation of single safety factor and reliability index under seismic condition. The research results show that the bringing exceeding probability into dam slope stability calculation can increase the value of reliability index to match the engineering practice compared to consider earthquake as deterministic events and can match the allowable factors of safety in specifications