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Using the conventional observation data，precipitation data of automatic weather stations and NCEP 1°×1° reanalysis data, we comparatively diagnose two heavy rainfall processes happened in the middle South Xinjiang on 14 April 2017 (4〖DK〗·14) and 1 to 2 May 2017 (5〖DK〗·1), the similarities and differences in meteorological dynamics of two spring heavy rains are discussed. The results indicate that the spring heavy rains occurred in a background of the active subtropical westerly jet, the northward extended Iranian subtropical high, the active ground cold front, and lower and upperlevel jetfront systems. The water vapor was from the Arabian and Caspian sea of around 40°E， which came into Xinjiang followed by west winds， and then converges at the middle South Xinjiang with the favorable wind condition. The upperlevel and lowlevel jets were coupled to form the secondary vertical circulation, and dry and cold air invasion prompted the atmosphere instability and precipitation intensity. The main differences between two processes are: the subtropical westerly jet was abnormally shifting northwards at 500 hPa, resulting in the shortwave trough and the cold air from western at surface in the April rainfall. While the polar front jet and the subtropical westerly jet were joined together at 500 hPa, there existed a long wave trough and cold air from northwest at the surface in the May rainfall. The April rainfall is a typical jet stream front type rain with convection precipitation, during which there were two secondary vertical circulations formed, with the lower one caused by three cold air flows from different directions, triggering the nearby cyclonic circulation at 850 hPa.The May rainfall is a typical jet stream with cold front， in which the downward incursion of upperlevel cold air triggered a powerful integrated secondary vertical circulation and enhanced the precipitation.