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A total of 31 precipitation cases in July and August 2007 over the Qilian Mountains are classified on the basis of the dominant air currents at 500 hPa and the cloud pattern of FY2D satellite images，taking the difference between 110°E and 90°E of the mean 500 hPa geopotential height of the grid points in 30° to 45°N as the classification standard.The precipitation cases can be classified as three main patterns: southwest current，northwest current， and flat west current.The southwest current pattern is divided into two subtypes: moving and blocking; the northwest current: cold advection and Hetao cold vortex.On the basis of data of the mesoscale automatic weather station network over the experimental region， the relation of precipitation with altitude and slope direction is discussed.The circulation characteristics and precipitation intensity of each circulation pattern that generated precipitation are analyzed. It is found that different largescale circulation patterns will result in different topographically forced mesoscale systems due to topographic dynamic and thermodynamic effects.