Abstract: It is proposed in this paper that the discharge coefficient K,x in Muskingum Flood Routing Method based on long-term flood routing can also be used on the short-term one of the same river reach. Thus, some special demands in water conservancy and hydroelectric design as well as the approximate calculation problems of unsteady flow for daily-regulation of the hydropower station are resolved. The physical foundation of this method is assuming the riverbed as a prism. The analysis of observed data shows that this method meets the requirement in planning and designing work of projects with higher calculation precision.