Abstract: In this paper, the contrast study of different cold-air forces has been done in large-scale circulation, meso-scale systems and vapor budget for two heavy rainfalls in Yunnan during early summer. The results show that the two courses which had similar large-scale circulation, were the result of interaction between Indian-Myanmar trough and East Asia cold (thermodynamic) trough, but the force of cold and warm air was different from each other. The stronger the cold air was, the more convenient for the meet of cold and warm air in Yunnan. The development of the mesoscale convergence lines in the lower part related to the force of the cold air. The topography of Yunnan had influence to mesoscale convergence lines when cold air wasn’t strong enough. The precipitation position only related with mesoscale convergence lines. The analysis for the frontogenesis of the two processes shows, the location of frontogenesis could reach upper troposphere when the cold air was strong enough. Otherwise, the cold air entered into Yunnan only along the topography. Furthermore, the cause of the two heavy rainfalls related with the interaction between lower and upper jet. The analysis for water vapor supply shows that main water vapor source of heavy rainfall may come from Bay of Bengal. Meanwhile, water vapor could be brought to middle troposphere under strong intercourse between cold and warm air, and then caused heavy rainfall.