Abstract: In this paper,the advantages and shortcomings of empirical orthogonal function have been discussed.This function was applied to the diagnostic analysis of "plum rains" in China.The results indicate that the empirical orthogonal function is useful in the diagnostic analysis.With this approach the results which are in agreement with synoptic analysis can be obtained.This is a statistical method.It would play a greater role in weather analysis and forecast,if it is combined with synoptic and dynamic methods.