Using the 19482012 NCEP/NCAR global grid daily average data, SCSSM onset dates (retreating dates) are determined to be at the pentad when the average zonal wind, which is from sequences of onset and retreat dates for nearly 65 years, steadily changes from east to west (west to east) and the pseudo-equivalent temperature is steadily within o_(se)>335 K (o_(se)<335 K) at 850 hPa in a key zone of the South China Sea (110 ?120 °E, 10 ?20 °N). Analysis shows that the clockwise vortex of the equatorial Indian Ocean region has similar guided influence on the cross-equatorial flow and the subtropical anticyclone on the outbreak (retreat) of the SCSSM. The onset date of the SCSSM is closely related to its intensity, and with late (early) onset of the summer monsoon, its intensity is strong (weak), and the abrupt change of zonal wind is early (late) in the upper troposphere. Climate warming has an important influence on SCSSM; with the onset date earlier, the retreat date will be later and the intensity will be weaker.