The onset and advance of the South China Sea summer monsoon affect the process of the summer rain belt in China. The NCEP (National Centers for Environmental Prediction)/NCAR (National Center for Atmospheric Research) reanalysis data are used to analyze the characteristics of changes in the South China Sea summer monsoon before/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 700 hPa) 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 southwest wind carrying water vapor from the Bay of Bengal into the South China Sea through the Indo-China Peninsula shows a decreasing trend, and the decrease in water vapor entering South China from the South China Sea leads to spatial differences in precipitation trends 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 of South China is strengthened, while the influence on the north of the South China Sea and Southwest China is weakened.