Based on the satellite GMS data, FY satellite data and the hourly precipitation data of Guangxi from 1984 to 2013 and using the statistical analysis, the comprehensive analysis and the typical case study methods, the evolution characteristics and propagating mechanism of the convection over the Bay of Bengal before continuous torrential rain occurs in Guangxi are investigated. The results show that the convection over the Bay of Bengal is enhanced abnormally 2-3 d before the occurrence of continuous torrential rains. So the strong convection over the Bay of Bengal is a precursory signal to the vortex shear continuous torrential rain in Guangxi. This precursory signal can guide the short and medium term forecasting of torrential rain in Guangxi. This study conclusion shows that the convections over Guangxi are highly correlated to the convections over the Bay of Bengal. The strong convection eastward propagation channel exits between the Bay of Bengal and Guangxi.