Based on the daily precipitation data of 753 stations during 1961-2011 provided by National Meteorological Information Center of China and the NCEP/NCAR 1961-2011 daily wind and specific humidity data,this paper investigates low-frequency characteristic of the multi-year mean summer precipitation in South China and its relationships with low-frequency water vapor transport.Results show that summer precipitation in South China has the tendency of increasing,and is obviously more after 1992(1993-2011,period Ⅱ) than before(1961-1992,periodⅠ),especially in most Guangxi,northern Guangdong and the boundary beteen Fujian and Jiangxi.Summer precipitation in South China shows significant 10-20 d low-frequency oscillation,which is more significant in the period Ⅱ than in the periodⅠ.In periodⅠ,the anticyclonic water circulation in northwest Pacific and a pair of cyclonic and anticyclonic water circulations in east of the Indo-China Peninsula and south of South China Sea are the main systems affecting 10-20 d summer rainfall,with water vapor mainly from the bay of Bengal,South China Sea and west Pacific,and cold air from Caspian Sea and east of Lake Baikal.In period Ⅱ,a pair of cyclonic and anticyclonic water circulations in northwest Pacific and in east of Indonesia are the main systems influencing the low frequency rainfall,with water vapor from South China Sea and west Pacific and cold air from east of Lake Baikal.