Abstract: In this paper, using winds of 850hPa from NCEP reanalysis and OLR, the variations ofboth SW wind components and OLR over South China Sea (SCS) and the relations between themare discussed. An index of the SCS summer monsoon is proposed. The features of intensity andonset time of SCS summer monsoon are analyzed. It has been found that the seasonal variationsof SCS summer monsoon pessess the characteristic of two-peak pattern. The intra-annual variations of,intensity and onset time are linked with the SST anomalies. SCS summer monsoon willstart early and be strong in El Nino year, it is reversed in La Nina year.