The eleven persistent heavy rains occurred over southern China during 5 May to 27 June in 2010. By using NCEP/NCAR daily reanalysis data, the causes for persistent heavy rains are analyzed. The results show that the Ural blocking high, Baikal low trough and the West Pacific subtropical high are stronger than the normal, and they are successively and stably maintained. The strong southwest air successively meets with the dry cold air from middle and high latituded in southern China. The low vortex which continued to move eastward is the important heavyrainproducing mesosacle convective system. The strong ascending flow resulting from the instable warm air and the strong vapor flux convergence are the favorable heavyrainproducing conditions.