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The analysis and summary are made of the 20 rainfall events occurred around the Qilian Mountain from 2002 to 2004 by use of the reanalyzed daytoday 6h NCEP/NCAR data. The results show that there was a upperlevel westerly jet from east to the west at 40°N, 200 hPa; precipitation generally took place in the south side of the jet axis, and there was cold downdrafts on the north side of the jet axis, warm and humid upcurrent on the south side, and the subcirculations beneath; there was strong divergent ascending motion on the right side of the entrance area of the jet axis, and accordingly there existed strong convergence ascending area at the lower levels. The collocation of divergence and convergence at the upper and lower levels is beneficial to the formation of strong convection weather. The existence of the westerly jet axis at high altitudes is of profound influence to the precipitation over the Qilian mountain areas, and the position variation of the jet axis affects the location of the precipitation.