Precipitation is one of the key inputs in the hydrological process and has a decisive influence on the hydrological response of the basin.However，due to the influence of factors such as topography and climate，rainfall presents spatial heterogeneity.Selecting the Hengjiang Basin，which is located at the junction of Sichuan，Yunnan and Guizhou provinces.The topography is relatively complex and the spatial distribution of rainfall is uneven.Based on the measured data of the rainfall stations from 2009 to 2011，calculating the spatial inhomogeneity coefficient of the basin and simulating the hydrological process by using the Xin'anjiang model.The results show that the spatial distribution of rainfall has a great influence on the hydrological simulation of the Hengjiang Basin.The spatial distribution inhomogeneity coefficient Cv and the NSE value of Xin'anjiang simulations present a quadratic function relationship.As the rainfall inhomogeneity decreases， the model accuracy will decrease.It is not the case that the more uniform the rainfall data，the better the results.This study has important theoretical and practical significance for understanding the role of rainfall spatial heterogeneity in conceptual hydrological models，especially how to effectively consider spatial changes in simplified hydrological models.