Abstract: In this paper the northern winter 100hPa teleconnection patterns are studied, discovering that there exists a PNA flow pattern at 100hPa in northern winter with its wave train quite similar to that of the 500hPa flow pattern. When El Nino is at the prime of the season (in winter), a vigorous PNA pattern occurs at 100hPa at better corresponding rate than at 500hPa. In addition,studies are made of the 100hPa tropical wind field for the stages of El Nino formation and development and the mean circulation anomaly at 100hPa in the four seasons (spring、summer、autummand winter).revealing that in the spring of El Nino years,the 100hPa height is lower over a large area than in the La Nina years; similar significant features are seen in preceding winters. The results are used to diagnose the El Nino events in 1991-1992.