Abstract: The slope shape has a significant effect on the surface stress state of slope, and the stress state is closely related to the slope stability. The previous rainfall infiltration model only takes the slope with straight line shape into account, and did not include the slope with curve shape. Combining Mein-Larson infiltration model with slope shape function, the infiltration function of concave slope under rainfall is deduced. Combined with limit equilibrium analysis method, a calculation model of concave slope stability is proposed. At the same time, according to the idea of slope shape fitting and slope shape simplification, the actual slope is studied as concave slope and straight slope respectively. The results show that the infiltration depth of wetting front has a linear relationship with rainfall time, and the wetting front is paralleled to the slope at different rainfall time. When the actual slope is analyzed as a concave slope, the rainfall infiltration law is more in line with the actual situation; when the rainfall time is 10 days, the calculation result of the shallow slope model is 0.95, while the stability coefficients of the calculation model and the numerical simulation are 1.004 and 1.003 respectively, and the relative error is not more than 1%. Therefore, compared with the previous calculation model, this model not only takes the actual slope shape into account, but also has the characteristics of simple calculation and high reliability.