Abstract: Based on the daily observation data,satellite images of FY-2C and NCEP 1×1°6 h interval reanalysis data,a heavy rain event on December 11th,2010 which occurred at middle and south of Yunnan Province has been nalyzed.Results show that the heavy rain weather process in winter occurred at a favorable circulation background,ITCZ whose position was northward was comparatively active;a cluster of convective cloud existed at Bay of Bengal, a branch of abnormal southwest flow existed in Indian Ocean around 10°N;a tropical cyclone generated on low-layer at Bay of Bengal which presented cyclone-type on satellite images;the tropical cyclone at Bay of Bengal,southern trough around 90°E and southwest jet at low-level in the front of southern trough moved eastward causing the heavy rain weather process;the water vapor and energy which caused heavy rain transporting from Bay of Bengal by low-level jet,plentiful vapor was strongly converged at Yunnan province,θse shows vertical shape along heavy rain area,heavy rain occurred at the regions of upward motion which lower layer convergence and higher layer divergence,the convergence region of moisture flux divergence and wet Q vector was well coincident with the heavy rain region.