Based on data of convention observation, NCEP 1°×1° reanalysis, ground-based observation, wind-profile radar in Lianyungang and Doppler weather radar, heavy rainstorm process on August 10, 2012 was analyzed. The result indicated that after landing in the southeast Anhui, typhoon "Haikui" weakened into a tropical depression. The combination of inverted trough stretching towards the north and upper-level trough was found to be the background of the heavy rainstorm happened in the northeastern Jiangsu. Its ambient field was characterized by extreme unstable atmospheric stratification, moisture convergence center, convergence trough, upper-level divergence center and powerful ascending motion. Cold air penetrated into the meso-sphere and upper-level from the lower atmosphere, which triggered the release of instable energy. The lasting of medium-scale convergence line was the main reason of this heavy rainfall event. Wind convergence, cyclonic circulation, mesocyclone signature,low-level jet,warm advection and greater radial wind field were revealed in the medium-scale environmental field signature during the torrential rain. According to these facts, the nowcasting of occurrence and maintaining of heavy precipitation is available.