The precipitation characteristics over the South China Sea are analyzed by using daily station rain gauge data and the Tropical Rainfall Measuring Mission 3B42 product. It is found that rainfall over the South China Sea is at the maximum seasonal level in autumn, particularly from August to October, which is different from rainfall over most of the other regions in mainland China. Further analyses show that a subtropical high of 500 hPa and sustained low-level depression systems are key factors in the formation of autumn rainfall over the South China Sea. In addition, the location of the subtropical high is greatly influenced by sea surface temperature over the tropical Pacific Ocean. The rainfall amount over Hainan Island from August to October is highly correlated with the simultaneous and lead Niño3.4 indexes and the correlation coefficients between them can reach －0.47 and －0.43, respectively. As a result, the Niño3.4 index can be used for rainfall climate prediction during the August to October period over Hainan Island.