In an all-round way was made a contract analysis of the flood series of 60 large conservancy projects in the country by means of multiplaying frequency curve of type Ⅱ(X-Ⅱ) and type P-Ⅲ. It is proved that type X-Ⅱ would possess the condition to use in projects, for it has more advantages than type P-Ⅲ.