Abstract: In order to analyze the impact of rainfall on the inundation process before and after the sponge transformation in temporal and spatial scales, a numerical model that couples hydrology and hydrodynamic processes on the surface and pipeline network is adopted, and the second bid section of Xiaozhai sponge reconstruction is taken as the research site. The city inundation process during the recurrence period is simulated using different design rainstorms, and the inundation has been compared in time and space scale. The results show that compared with the peak time of heavy rain, under the design rainstorm return period of 2 a, 5 a, 10 a, 20 a, 30 a and 50 a, the smaller the design rainstorm return period, the more significant the effect of sponge reconstruction on the delay time of the peak lag time of the total urban inundation water accumulation and the peak inundated area. And all show a decreasing trend as the return period increases. The maximum delay time of the former is 0.133 h and the minimum is 0.117 h; the maximum delay time of the latter is 0.084 h and the minimum is -0.016 h; With the increase of the return period, the total amount of inundation water and the peak inundated area after sponge transformation have gradually increased and stabilized compared with the reduction before sponge transformation. In the decreasing trend, the former is 71.37% at the maximum and 22.76% at the minimum; the latter is at 68.87% at the maximum and 15.08% at the minimum. This research is helpful for more accurate and effective prevention and control of inundation, accurate forecasting and early warning of urban inundation, providing effective information for urban and rural residents to travel, and reducing loss of life and property.