Based on FY-2C meteorological satellite data and several physicsfield s calculated by NCEP/NCAR reanalysis data, the causation of the heavy rainfall event on August 16, 2005 in Tianjin is analyzed. This event occurred in a cold front with trough. And the infrequent rainfall was produced by the reasonable allocation o f the trough and the subtropical high in the middle troposphere, the shear line in the low troposphere, the incursion of the cold air in the surface, the strong instability energy in the lower / middle troposphere and the sufficient water v apor. The mesoscale characteristics of the event are associated with the mesosca le convective cloud clusters. At the same time, another convective cloud cluster s with weak precipitation but strong convection in the northeastern Heb ei Province, Beijing and Tianjin on the 15th are compared and analyzed. There are some differences between them in environmental conditions of their formation a nd development. It could provide some forecasting information for two kinds of weat her in the future.