Abstract: According to the formation conditions of "7·20" extremely heavy rain in Zhengzhou City, the heavy rain similar to "7·20" extremely heavy rain in Zhengzhou City happening in Hefei City is possible. In order to deeply learn the lessons of the heavy rainstorm disaster, makes an assumption that the "7·20" heavy rain conditions in Zhengzhou City happens in Hefei City, and carries out simulation calculation and flood analysis to provide reference for preventing such heavy rain and flooding, and improving the over standard flood emergency plan and urban flood control planning.