Abstract: Because Green-Ampt model is too simplified to accurately calculate the total infiltration volume, we propose an improved Green-Ampt model which conforms to the actual infiltration law in this paper. The proposed model divides the soil profile into saturated, transitional saturated and natural saturated zones. A soil column test is performed to verify the accuracy of the proposed model and the existence of transitional zone. Three indexes are used to evaluate the accuracy of the model. They are the mean absolute error(MAE), the mean absolute relative error(MARE) and the root mean square error(RMSE). The MAE, MARE and RMSE are smaller than those of the classical Green-Ampt model. As a result, the accuracy of the proposed model is higher than that of Green-Ampt model. The proposed model is also used to analyze the stability of an unsaturated soil slope. The calculated results show that the slope angle and precipitation rainfall intensity are inversely proportional to the slope safety factor, and the former has a greater influence impact on the slope safety factor. Compared with the proposed model, the Green-Ampt model underestimates the slope safety. The improved Green-Ampt model provides references for analyzing the risk of rainfall and landslides.