Reliability analysis is one of the hot topics in the research of slope engineering. The authors mainly analyzed slope reliability based on finite-difference strength-reduction method considering the thought of Monte Carlo method. The principle and statistical model of slope reliability analysis are elaborated at first. Second, the finite-difference strength-reduction method and the thought of Monte Carlo method are summarized, then the thought of Monte Carlo method is introduced into the finite-difference strength-reduction model. Based on this, numerical calculation of the model was realized and the corresponding calculation program was developed by FISH language built in FLAC3D. Finally, safety factor of a slope, whose rock mass mechanical parameter followed normal probability distribution, is calculated. The calculation results were analyzed statistically and its reliability is evaluated.