Abstract: Analysis is undertaken of spatial-temporal distributions of autumn rainfall over Shaanxi in 2003, as well as the synoptic and thermal features of atmospheric circulation, indicating that the fallout zones and time are relatively concentrated, rainfall intensity is great and duration is prolonged, which is the most severe event ever observed since 1954. In the transition from a summer to a winter pattern of circulations, with upper troposphere westerly jet moved southward to 400N, areas on the northeast side of the northeast side of the Tibetan Plateau including eastern NW China in which is located Shaanxi are under the control of upper-air divergence to the south of the jet and the areas have high temperature and rich moisture in lower levels, answerable for active rising motion, leading to a mechanism for lower-convergence and higher-level divergence. At this site a relatively stable situation is kept for 500 hPa circulations over Eurasia. A stronger and more eastern and western subtropical high has its outer-region southerly flows responsible for transporting large amounts of vapor, thus leading to a spell of continuous overcast and rainy weather in the northwest part of the country, which comes to an end when a midlatitude Xinjing high is established and subtropical high moves eastward and retreats toward the south.