Abstract: Taking the Gudongkou Reservior catchment in Xingshan county, Hubei province as an example, firstly, using the precipitation data from 1997 to 2016, we analyzed the distribution features of heavy precipitation in 3 h, 6 h, 12 h and 24 h time scales. Secondly, choosing the Xin´anjiang hydrological model, we determined hydrological model parameters through the simulation of 40 historical flood cases. Thirdly, based on the simulation results and the flood-preventing capacity of reservoir, we calculated the flood critical area rainfall, that is, the flood limit water level needed reaching the critical area rainfall in different baseline levels and time scales. The results show that it is feasible to use hydrological model to calculate critical area rainfall getting the flood process and water level variation curve in different time scales and base water-levels. It is proved that when the initial condition (base water level) is the same, the smaller the time scale is, the smaller the critical area rainfall is.