Abstract: In this paper the correlation analysis,factor analysis,fuzzy classification.,and principal component analysis (PCA) are performed for the southern osciliation index (SOI) from the Ciimate Analysis Center (CAC) at the NOAH.It is shown that the 12-month SOI can be classified into two groups:one from January through April and the other from May through December.They differ in persistency and correlation.It is also found that the year of strong or weak SO can be defined by the first principal component of the SOI.In addition.the relations beiwaen the SOI and 50p hPa geopotential height,mean monthly zonal height,mean monthly interzonal height differences,centers of atmospheric activities,characteristics of the atmospheric circulation int period of 24 months from January through December of the neat year have been.examinated based on the monthly data from 1951 t hrough 1984.Analysis indicates that in the early part of the low SOI year,i.e.,in April,the 500 hPa geopotential height north of 75°N is significantly low and then becomes higher in May.It is found that in April the trough of the first harmonic wave is in the eastern hemisphere and the contribution of its variance is smaller than in May.Analysis shows that the opposite is true in the high SOI year.Such variation in the height field during the April-May period is an early signal of the SO at higher latitudes.In the end,a statistical prediction model for the SOI is presented,by means of which a low SOI year as well as an E1 Nino event has been successfully predicted for 1986.