This paper focuses on the new developments in the rainfall-runoff model of the hydro-informatic modeling system(HIMS). The original rainfall-runoff model of HIMS is the LCM model, which is based on the dynamic rainfall infiltration mechanism and has been built through a large number of field observation experiments in small watersheds. In order to further understand the physical mechanism of the LCM model, the HIMS research team proposes a new GAF model based on the Green-Ampt model whose physical mechanism is clear. Theoretically, the LCM model and the SCS-CN model can be directly derived from the GAF model, it is proven that the LCM model is a high-accuracy power exponent approximation of the GAF model, and that the SCS-CN model is a simplification of the reciprocal linear approximation solution of the GAF model. Based on deep analysis of the analytical solution of the GAF model, a modified SCS-CN method with two new parameters, which considers the impact of rainfall intensity, is proposed.