The Bay of Bengal is known as a breeding ground for tropical cyclones. The storm activities in the Bay of Bengal have considerable impact on the weather over the Qinghai-Xizang Plateau and southwestern China. In 2007, cyclone Akash (0701) resulted in a continuous precipitation event over southwestern China during May 15-17. In this study, the mechanism of heavy rainfall induced by Akash is investigated based on precipitation data from NOAA, NCEP/NCAR reanalysis data, and satellite TBB data from JMA (Japan Meteorological Agency). We found that heavy rainfall occurred when Akash interacted with a westerly trough over the Tibetan Plateau. The cloud clusters that separated from the Akash cloud system ascended in a northwardly direction to the lower latitude plateau strengthening the trough clouds and causing extremely heavy rainfall. Influenced by the strong divergence at the upper levels of Akash during its northward movement, the South Asia high strengthened, moved northward dominating the area over southwestern China, which enhanced the upper troposphere divergence, and in turn, strengthened Akash’s ascending motion. The storm transported large amounts of water vapor to the heavy rainfall area. The net inflow of water vapor, the growth of moist baroclinicity, and the strong conditional symmetric instability were all favorable for the development of this heavy rainfall event. We also found that the low-altitude plateau topography increased the ascending motion by forcing an uplifting southerly flow, which enhanced the heavy rainfall.