Abstract: Based on the NCEP/NCAR reanalysis product and GPCC (Global Precipitation Climatology Centre) rainfall data, the relationship between Somali Jet intensity and rainfall over Southwest China is investigated in this study. The results reveal that rainfall in the early summer (May) over Southwest China is closely related to Somali Jet intensity. When the Somali Jet is stronger than normal, the May rainfall over Southwest China is larger than normal, and vice versa. Further studies show an obvious decadal variation in the relationship. In fact, the stable relationship between the Somali Jet intensity and May rainfall over Southwest China has been established since the 1980s. The convergence of wind fields at low levels in the atmosphere is a key general circulation pattern for the May rainfall over Southwest China. Before 1980, the Somali Jet intensity was only related to southwesterlies over the region from the Bay of Bengal to southern China. However, it is closely related not only to southwesterly flows to the west of Southwest China but also to northeasterly flows to the east of Southwest China after 1980. This is a possible reason for the establishment of the relationship between Somali Jet intensity and May rainfall over Southwest China.