Abstract: Yunnan is a typical monsoon climate area located in the low latitude highland in China, affected by South Asia monsoon and East Asia monsoon at the same time. The heavy rainfall in Yunnan has peculiar area characteristic because of special geographic location and landform. In summer, the landing westbound TC from the South China Sea is one of the most important weather systems causing heavy rainfall in Yunnan. Statistics indicate the extreme heavy rainstorm in Yunnan is mostly caused by weaken landing TC, so its important to research mechanisms of landing TC heavy rainfall on the plateau. In 2006, the typhoon class TC Prapiroon, lands westbound and weakens into tropical depression in Yunnan without causing heavy precipitation. But in 2008, another TC Kammuri of the same strength causes eight days continuous precipitation, and a two day course of large-scale heavy precipitation in Yunnan Province. With the conventional observation data, best track data of CMA-STI and FY-2C satellite images and TBB, the precipitation caused by Prapiroon (0608) and Kammuri (0809) are compared on track, rainfall, speed, the circulation and hydrodynamic field. The result shows that they have similar birthplace, track, landing place, affecting time and central precipitation falling area, but Kammuri has much greater impacts on the length of time, the scope and impact of disasters. Active southwest monsoon and ITCZ, southerly low level jet, westward moving subtropical high and convergence ascending region, contribute to the major weather background of tropical cyclone precipitation in Yunnan. Effected by a variety of systems together, the typhoon circulation is very durable, resulting in the formation and maintenance of MαCS and MβCS clouds, leading to the occurrence of precipitation. Diagnosis on these physical fields shows that as a result of the active monsoon system, the Bay of Bengal and the South China Sea constitute a powerful water channel, through which instability energy and water vapor are transported to Yunnan accompanied by the establishment and enhancement of low-level jet. CSI and deep convection of positive feedback mechanisms lead to heavy precipitation in Yunnan.