Due to the dynamic storage characteristics, traditional flood routing method of static reservoir capacity is no longer applicable for determination of the highest water level of the Three Gorges Reservoir (TGR) during the flood routing model. Therefore, research on the new method is needed for deriving accurate water level forecasted value. When the water level of the reservoir rises to the highest point in a flood event, flood routing in the TGR region reaches a critical state. At that time, a reasonable correlation between storage capacity and water level is expected to be established under the constant inflow and discharge condition. In order to quickly calculate the highest water level in flood routing for TGR, based on the hydrological model coupled with hydro -dynamic model, a dynamic reservoir capacity curve which uses the inflow and discharge as parameters was built and 16 flood hydrographs were employed to test its effects. The results show that the mean deviation between the measured values and calculated values is only 0.20 m, which proves the established highest water level calculation method has a good practical value.