[Objective] The objective of the study is to evaluate the instability probability of shallow landslide induced by rainfall, and to provide theoretical basis for related research. [Methods] We combine Mein-Larson model with infinite slope stability models of saturated soil by introducing and developing the Mein-Larson infiltration model, and establish deterministic models for rain-induced landslides under short duration rainfall with high intensity and long duration rainfall with low intensity. Then we establish a probability analysis method of the slope instability by combining the deterministic models with Monte Carlo method. [Results] One kind of evaluation method for the failure probability of shallow landslide induced by rainfall was proposed.[Conclusion] The probability method not only can describe the uncertainties in the process of occurrence and development of rain-induced landslides, but also can calculate the instability probability of rain-induced slope instability under the different rainfall time. The assessment results are in high agreement with the actual slope.