The characteristics of sea surface temperature anomalies (SSTAs) in the tropical oceans and their influences on the onset of South China Sea summer monsoon (SCSSM) have been studied. The anomaly of SST in tropical Pacific Ocean exerts persistence impact for one to three months on atmospheric circulations. If the warm pool becomes anomalously warmer during an earlier period from February to April, the SCSSM breaks out earlier, and vice versa. Singular value decomposition (SVD) and composite analysis have shown that, in La Ni?a pattern, the convection over Western Pacific will occur earlier and be stronger than normal, which favors the convergence at a lower layer over Western Pacific, as well as the strengthening of upwelling branch of Walker circulation, leading to an earlier burst of westerly in the southern South China Sea. Moreover, the convection in Sumatra appears earlier than normal and favors the westerly evolution in eastern Indian Ocean, resulting in the splitting of the subtropical high belt and an early onset of SCSSM. However, the atmospheric circulation anomaly is reversed in El Ni?o pattern.