This paper mainly takes PanShiTou Reservoir as the research object, adopts the three water sources Xin'anjiang model to forecast and analyze the two floods of 850704 and 860520, and selects the rainfall data of six rainfall stations for these two floods, and adopts the three water sources Xin'anjiang model to carry out evapotranspiration calculations, flow production calculations, sub-source calculations, and confluence calculations to derive the predicted value of the flood, and then compare the predicted value with the actual value, and then analyze the error analysis of this study. Comparing the predicted values with the actual values and comparing the error analysis of this study, it is concluded that the prediction level of these two floods is C. This study provides an effective technical means for the flood prediction of reservoirs and provides essential support for the operation and management of reservoirs.