In order to combine forecsts made with several methods with an optimizing forecast,a technique of combining forecast,which is called an optimal blending method,is suggested.The technique considers both a persistence forecast and systematic errors existing in the methods.A hindcast data the for years was established.Then a linear model was set up with the data set.The test for the precipitation field in summer(June,July,August) was conducted.It shows that the optimal blending method can improve the forecast skill significantly,but the skill varies year-to-year.