To investigate the spatial distribution of runoff under heavy rainfall scenarios in Chengkou County, Chongqing Municipality, and to provide reference for local disaster prevention and mitigation. To simulate the runoff volume under six rainfall scenarios with 24-h rainfall amounts of 50, 75, 100, 150, 200, and 250 mm through the improved SCS model, coupled with data on soil type and land use, and to analyze the distribution of runoff volume in each township of Chongqing Municipality. To select four representative heavy rainfall scenarios for runoff volume spatial simulation in 2010 and 2020. The results show that: rainfall runoff in Chengkou County is statistically positively correlated with rainfall; with the increase of simulated rainfall, the runoff volume increases in a non-linear step, and in the area with larger CN value, the runoff volume increases faster, and the risk of flooding increases; in the same rainfall intensity, the higher runoff volume area is mainly distributed in the southwestern townships of Chengkou County; the changes in rainfall runoff are closely related to the changes in land use. Land use changes affect the rainfall runoff volume by changing the size of the CN value; the simulation results of four actual rainfall events show that Shuanghe, Zhouxi, Mingtong, Gecheng, Xiuqi, Heyu, Dong’an, and other townships in Chengkou County are the key preventive areas for heavy rainfall and flooding. The above research results can provide support for heavy rainfall and flood disaster forecasting and warning in Chengkou County.