In recent years, extreme weather events have been frequent, and the suddenness and extremeness of flood disasters caused by rainstorms have become more and more significant. Most areas in Haihe River Basin have not experienced extreme floods for decades. To be well prepared for the disaster of extreme flood that might happen in this area in the future, it is necessary to carry out the prediction of rainstorm center and the analysis of possible regional flood composition. Taking the Daqing River as the study area, which is unafflicted by extreme floods for many years, we predicted the possible location of the rainstorm center of the river system, based on the precipitation data of 103 rainfall stations in the study area, and then carried out the transplantation of the rainstorm center and the analysis of regional flood composition, with the distribution of rainstorm “63·8” as the reference. The results indicates that the rainstorm center is relatively fixed in Daqing river, which is likely located at the altitude between 100 and 600 m. Under the same precipitation condition, when the rainstorm center is located near the mountainous area downstream of the reservoir (which is the case for “63·8”), the total volume of flood is relatively large; when the rainstorm center is located near the plain area, the total flood volume is small, and the change of the rainstorm center location has a significant impact on the regional flood composition.