By using mainly GMS pictures, together with radar echo and ground data, this paper analyzes the relation between the development of heavy rain cloud clusters in 0-6 hrs before 50 heavy rain occurrences in the regions of the Three-Gorges and Jingjiang River, and the large-scale environmental cloud field. Established according to different trigger mechanisms are five types of concept models, cold front, stationary front, convergence north of the front, mesoscale occlusion and arcus line related to typhoon, upon which criteria are provided for nowcasting heavy rain. Satisfactory effects have been achieved in the operational tests in the period of June-August, 1989.