With more and more water projects have been built,the study focus of flood control planning and dispatching has been diverted from single project to a complex group of reservoirs in whole basin.With the development of computer technology,the random analog technique has been applied to simulate runoff and accurately describe the hydrologic characteristics of a complex catchment. This paper discusses the defects between conventionalhydrology method and random analog technique.A new method is given to simulate flood in a catchment,which hasbeen put to use of a group of the reservoirs in Taizihe River Basin,and has gained a better result.