Abstract: Located at southeast coast of China, the Xixi Basin is a mountainous river basin, and floods rise and fall steeply. Flood forecasting under the influence of typhoon and rainstorm is an important issue for flood prevention and mitigation. In this paper, the iterative asymptotic method was used to calibrate the key parameters of the HEC-HMS model with the flood events of the largest annual typhoon rainstorm flood from 2003 to 2012. An empirical relationship was established between the initial loss rate of the calibrated model parameters and the initial discharge, wave velocity and the maximum rainfall intensity. Then the relationships were verified with the largest annual flood from 2013 to 2015. The results showed that:①HEC-HMS model has strong applicability for the typhoon rainstorm flood in Xixi Basin. There are 9 calibration period floods, only 2 floods, the relative error of peak discharge is greater than 20%, The peak time difference is within 2 h, and the average efficiency coefficient is 0.82; During the verification period, the peak discharge error and flood volume error shall not exceed 20%. ②It provides a new method to apply the model to flood forecasting. The correlation coefficients of the established empirical relationships between the initial loss rate and the initial discharge, wave velocity and maximum 1-h average rainstorm intensity are 0.956 and 0.899, respectively. By applying the empirical relationships, the model parameters can be determined through the forecasts of the initial discharge and the rainstorm intensity, and the flood process and the peak flow can then be forecast with the model.