Abstract: As a semi-empirical rule for estimating shear strength of integral rock or jointed rock masses, the Hoek-Brown failure criterion has been one of the most useful criteria in forecasting and stability analysis of rock masses strength. Three material parameters are included in the empirical formulas, such as m_b, s and a. practically, however, the three parameters are not be accurately calculated, they can be determined only through the middle variable or with geological experiences. In order to eliminate the accumulative errors during the middle derivation, eliminate the deviation of the slope stability assessment results, a new method is put forward. Taking the basic random variables, considering their variability and uncertainty, the reliability theory was used to analyze and evaluate the failure probability and reliability index for the slope. The reliability for jointed rock slope was based on generalized GH-B criteria, firstly from the four basic parameters of GSI, σ_ci, mi and D, the distribution of the variables was studied, and finally put into the H-B experience formula, the reliability calculation method was used to solve the failure probability. PEM as a highly efficient method, its results can satisfy the needs of the project. so, using the PEM to calculate the failure probability, through the analysis for a cutting pier slope, the results show that this method can improve the objectivity of the slope stability analysis, the result is more reliable.