Abstract: Based on the meteorological data from June to September, 1981~1991, a study on low- and mid-latitude circulation characteristics and moisture moisture transfer during the rainstorms period in the middle reaches of the Huanghe River is made by composite analysis. According to the circulation systems associated with 11 cases of extremely torrential rains, two types of rainstorm processes would be summarized. One appears in the flood season (mid-summer), another is in the early or late summer. The distributions of moisture flux, divergence of moisture flux and wind vector for the two types are analysed, respectively. The results show that there are great differences in the source regions, transport tracks and convergence intensities of water vapor between the two types of rainstorms.