An analysis is made of a persistent heavy rainfall process in Yunnan occurred from 18 to 20 in May 2004 by means of MICAPS data and FY-2 satellite cloud pictures. It is found out that main influencing weather systems include the Bay of Bengal Tropical Cyclone, shear line on 700 hPa, and cold front on the ground. The incursion of clod air into the periphery circumfluence of the Bay of Bengal Tropical Cyclone resulted in the strong development of the precipitation system. The plentiful vapor and strong ascending motion brought by the Bay of Bengal Tropical Cyclone, as well as the unstable atmosphere of high temperature and high humidity, provided favorable conditions for the development of the heavy rainfall. The maintaining mechanisms of the heavy rainfall also include the establishment and maintenance of the upper- and lower-level jets, and the continual triggering of strong frontogenesis.