Abstract: It has proposed a new method of correcting free-water storage based on dynamic system response in order to improve the real-time flood forecasting accuracy. Taking the part below the free-water reservoir of Xin'anjiang model as a system and connecting the disturbance of free-water storage with the corresponding system response difference, this method, has established an error inversion correction model, tracking back to the error source through the least square method, for free-water storage. It has been verified through the application of ideal model and Dongzhen drainage basin, and compared with the corrected results of AR(2) model. It is indicated that the correction effects of the new method is obviously better than that of the AR(2) model for the 16 floods happened historically to this drainage basin. Therefore, this method could be popularized in practical drainage basins.