The onset and advance of the South China Sea summer monsoon affect the process of the summer rain belt in China. In this paper, the NCEP/NCAR reanalysis data are used to analyze the characteristics of the South China Sea summer monsoon before and after global warming. The results show that the South China Sea summer monsoon is weakened after global warming, and the main features are as follows: 1) The average establishment time of the South China Sea summer monsoon is earlier, the average retreat time is delayed, the duration is longer, and the duration has an upward trend. 2) After the onset of the South China Sea summer monsoon (between June and September), the local circulation in the lower troposphere (below 700hPa) in the northwest of the South China Sea caused by the thermal difference between land and sea tends to weaken after global warming, and the southwest summer monsoon entering South China and Southwest China tends to weaken. 3) During the prevailing summer monsoon, the water vapor from the southwest wind and the Bay of Bengal entering the South China Sea through the Mainland Southeast Asia shows a decreasing trend, and the water vapor from the South China Sea to South China Sea decreases, leading to a spatial difference in the precipitation change trend in eastern China. 4) The South China Sea summer monsoon index shows that the influence of the South China Sea summer monsoon on the south-central part of the South China Sea and the east part of South China Sea is strengthened, while the influence on the north and southwest part of the South China Sea is weakened.