Various potential sliding paths and different failure modes should be considered in the stability of gravity dam against deep sliding when there are several faults. The safety factor of every fault is calculated with nonlinear finite element method, and the most possible sliding path is obtained by strength reduction method. The results indicate that the strength reduction factor is larger than the safety factors of all the faults. Based on the weighted regression response surface method, the reliability indices of the faults are computed and are compared with the safety factors, which shows there’s not an entire equity relationship between the reliability index and safety factor. Each failure mode of sliding path is a parallel system of several faults, and the final failure mode is the serial system composed of all sliding paths. The reliability of every sliding path and the final system are analyzed by means of the gradual equivalent linear method, and the results are consistent with the strength reduction factor. It’s recommended the reliability analysis be applied to the safety evaluation of deep sliding stability of gravity dams to make up the shortcomings of the safety factor method.