Abstract: The impact of sea surface temperature (SST) over the south China sea (SCS), Paci fic and Indian Ocean and their variations on the onset of summer monsoon over SCS is investigated based on fifteen years' (1982-1996) NOAA outgoing longwave radiation (OLR), wind and SST data from NCEP/NCAR reanalysis data set.It is found that region-averaged SST over the SCS is above 29℃ when summer monsoon bursts. The timing of monsoon onset is close to the date when the SST over south part of SCS reaches its maximum. The northward shift of warm pool plays an important role in the SCS monsoon onset. The deep convection activities usually occur in the region with large zonal gradient of SST. Therefore, the large zona l gradient of SST over SCS-West Pacific may be the reason why the Asian summer monsoon firstly bursts in this region.The annual variation in the SCS summer monsoon onset is closely related with SST anomaly. The early-onset years appear related with La Nina years and the delayedonset years related with El Nino years.