Abstract: The seasonal characteristics of mean pentad circulation over Asia at 500 mb level for each year from 1964 to 1978 are studied by the method of EOF, and a relatively objective method of division of NSS over East Asia is given in this paper. According to this method, each year over East Asia may be divided into 6 NSS, namely, Spring, Early and Middle Summers, Autumn and the First and Second Paris of Winter. The results agree with the conclusion in the paper (19) based on the mean multiannual data expanded by the same method. The mean circulations and synoptic features for each of these 6 NSS are analyzed and studied in detail.