Abstract: Large-scale accumulation slopes are widespread in the hydropower engineering constructions. The stability of accumulation slope has a great impact on the feasibility of the project and the safe operation. The accumulation horizon of complex composition has significant randomness and the parameters have variability. These characteristics make some uncertainty in the stability analysis of the stability of this type of slope. Based on probability theory, we use K-S test method to verify the distribution type of the physical and mechanical parameters. This method can reduce the influence of errors caused by artificial assumption. And sample the parameters respectively tested by K-S test method and artificial assumption method to obtain the state function and get the safety factor and reliability by using Monte Carlo Method. Comparison of two distribution type test methods, the K-S test method combined with Monte-Carlo method can improve the accuracy of reliability analysis effectively.