Based on the NCEP reanalysis data, black body temperature(TBB) data from FY-2E meteorological satellite, and routine and intensive automatic weather station data, a diagnosis and mesoscale analysis on the continuous Meiyu front heavy rainfall process in Jiangsu province from July 2 to 4, 2012 were performed. The results showed that the rainfall was caused by the confluence of the northeast vortex and the west Pacific subtropical high, positive jet and dry line. A series of 7 mesoscale clouds contributed to the rainfall, moving as a result of the "train effect". When the TBB of the cloud was below -64℃,the rainfall became heavy. The starting time of precipitation was 2-4 h later than that of the genesis of a mesoscale cloud. The surface mesoscale convergence system can be considered to be important indication of rain movement and intensity. The positive helicity at low level and negative one at high level, atmosphere of high temperature and humidity, high potential unstability, sinking motion compensation current and ultra-low-level jet all linked together into a configuration that brought about heavy rainfall.