Synoptic characteristics associated with heavy rain brought by monsoon trough in the latter flood season of Guangdong from 1981 to 2002 are analyzed. The result indicates that most of the cases take place when the Pacific subtropical high is inclined to the east or in lower latitude than its normal position and are directly related with the westerly troughs or ITCZs. Most monsoon troughs lie over South China or it coastal water. The divergence areas at 200hPa level usually cover the whole Guangdong or the most part of it with the divergence center over the offshore area of South China. The advancing northward of the monsoon is mainly resulted from the development of the trough over Southwest China and South China and the northward movement of the tropical cyclones. The southerly flows on the western periphery of subtropical ridge sometimes could steer the monsoon northward too. As a result, the convection tends to move from the South China Sea and Beibuwan Gulf and its neighboring area toward Guangdong and with a daily variation.