Abstract: Using pressure-energy technique, some cases of heavy rain in Changjiang-Huaihe river valley are investigated. It is found that the rain belts and heavy rain area are related to the dense pressure-energy belt. The triggering effect of pressure-energy on heavy rain is studied by using simplified divergence equation. The results show that inhomogeneity of pressure-energy distribution can trigger the quick reinforcement of convergence in the low energy side of the belt. Furthermore, the rain area can be estimated by computing the pressure-energy distribution.