Abstract: Areal rainfall is an indispensable input data for urban rainfall runoff simulation, considering the spatial heterogeneity of rainfall.And areal rainfall is closely related to rainfall station characteristics, calculation methods, and topography.To quantify the influence of rainfall station characteristics and spatial interpolation methods on areal rainfall calculation, Chongqing City, a typical mountain city, was selected as the study area, and six densities of rainfall stations were chosen.The spatial characteristics of rainfall stations were evaluated using the nearest neighbour index, and six spatial interpolation methods were used to assess their suitability for rainfall interpolation across different grades of precipitation.The results showed that with the increasing density of the rainfall stations, the error in areal rainfall calculation decreased.As the rainfall grade increased, the influence of rainfall station density on areal rainfall calculation became increasingly significant.When the number of rainfall stations was less than25,the simulation error generally increased as the uniform spatial distribution of stations increased.As the number of rainfall stations reached25,the more evenly station distributed, the smaller errors was.The Inverse Distance Weighted method and Radial-Basis Function method had less error in simulating areal rainfall in the northeastern mountains, while the Ordinary Kriging method was more accurate for simulating areal rainfall in the southeast.From the perspective of the describing ability of spatial distribution characteristics of rainfall, the Radial Basis Function method was the most suitable method for interpolation of areal rainfall in Chongqing City, especially in the mountainous areas.The results will provide a reference for selecting rainfall station data and areal rainfall calculation methods under different rainfall grades.