Abstract: In this paper,the evolutional procession of mesoscale precipitation system during a seldom heavy rainfall in Yangtze and Huaihe river basin from June 12 to 16 1991 is analysed,which is based on the conventional data,recording precipitation and wind data,radar and GMS-4 data.Some new observation facts of Meiyu front heavy rainfall was revealed,in which including "train distribution" and quick propagation of convective cloud core in meso-a system and some statistics features of meso-β convective system.