Abstract: An urban stormwater model was developed to analyze the hydrological response mechanism of effective impervious surfaces under urban stormwater simulation. The model focused on effective impervious area, and the Shuangqiaobang runoff-plot in Changzhou City was used as the study area. The model was calibrated using measured data, where the effective impervious area of roofs was first determined, followed by the remaining parameters. Different methods were adopted to characterize the imperviousness, and distinct simulation scenarios were set up to analyze the hydrological response of both the effective and total impervious areas. The results show that, the peak discharge and flood volume are overestimated when the total impervious area is used rather than the effective impervious area to characterize the imperviousness and when the parameters of the effective impervious area model are directly used; however, the peak discharge is higher in the low return period and lower in the high return period, and the flood volume is underestimated when a calibrated total impervious area model is used.