Abstract:Currently, under the background of the growing climate warming, extrem e weather events occur frequently. In order to understand the formation mechani sm of heavy rain and to improve the forecasting ability of heavy rain in the Hai he River basin, a synoptic diagnostic analysis for the heavy rainfall process in the Haihe river valley, especially in the east of Hebei Province, is performed with NCEP 6 hourly reanalysis data with resolution 1°×1°, the routine observ ation data and FY 2C satellite data. The results show that the heavy rain origin ated in the preliminary instable atmospheric convection region, and the stations which have 6 hour precipitation of more than 20 mm from 20:00BT of August 25th to 02:00 BT of August 26th almost located in the negative value area of the moist potential vorticity (MPV) in the low and medium layer of the troposphere. Mass of instable energy, heat and momentum were conveyed by low level jet (LLJ) to th e heavy rain region, which provided sufficient energy and moisture for the forma tion of the rain. The heavy rain region located at the western edge of the great positive value center of helicity. In the upper air of the heavy rain region there were strong rotating updrafts, and in the period of rain, convergence in underly ing bed, divergence in high level and the suction function that the latter was stronger than the former were advantageous in strengthening the underlying bed co nvergence and the convective ascending movement, providing favorable dynamic con dition for the formation of heavy rain. Simultaneously, the vapor in the high tr oposphere also played a crucial role in the development of strong precipitation cloud cluster.