Abstract: The basin urbanization can affect flood formation and confluence and significantly increase the difficulty in flood forecasting. In this paper, the HEC-HMS hydrological model is used to simulate the selected eight rainfall-runoff processes from 1980 to 1988 before urbanization in Qinhuai River Basin and seven rainfall-runoff processes from 2007 to 2013 after urbanization. Flood formation and confluence parameters under different land use scenarios were calibrated and the flood simulation schemes before and after urbanization were put forward for the analysis of watershed hydrological response to urbanization. The results show that the HEC-HMS model has good applicability in Qinhuai River Basin before and after the urbanization, and the simulation accuracy of the single-peak flood process is high. After the urbanization, other land use in watershed was transferred to urban construction land, so the watershed impermeable area increased significantly, leading to the increase of runoff and flood peak and 2 hours ahead of flood peak arriving.