Based on the data of MICAPS system, the abrupt heavy rain event in Dehong, Yunnan province on July 5, 2004 is analyzed. The result showed that the event had something to do with the establishment of Yunnan-Burma high. The low-level tropospheric jet supplied indispensable condition of high unstable geopotential energy and plenty moisture. Tibetan high southward moving and T-shape shear line and trough-line from east of Tibet to west of Sichuan province deepening and southeastward moving were helpful to guide northern cold-air mass moved southward. The strong moisture transportation and convergence and strong updraft, mesoscale cloud cluster stimulated by synthetical effect of cold-air, warm and damp air stream and particular terrain lead to the heavy rainfall.