Based on the NCEP/NCAR reanalysis monthly mean data and the precipitation data at 70 stations in Xinjiang, the relationship between the thermal anomaly contrast over the Tibetan Plateau and its surrounding areas in May and summer rainfall in Xinjiang were analyzed. By using the singular value decomposition (SVD) method, it was found that when the thermal anomalies were negative over the Tibetan Plateau and positive over the northwestern portion of the Tibetan Plateau, more summer rainfall occurred in northern Xinjiang. An index was defined to reflect the intensity of the large-scale thermal contrast between the two regions, and it was found that the thermal contrast between the two regions had a close relation with summer rainfall in northern Xinjiang. This relation is closer than that between thermal anomalies in any single region and summer rainfall in northern Xinjiang. When the index is negative, it indicates that the apparent heat source is weaker over the Tibetan Plateau and stronger over northwestern portion of the Tibetan Plateau. Under such a thermal pattern, (1) the subtropical westerly jet shifted further south; (2) an anomalous cyclone was located over central Asia and an abnormal anticyclone developed over Baikal Lake at 500 hPa, respectively. As a result, anomalous southerly winds prevailed over northern Xinjiang, which were favorable for the transport of warm and moist air from low latitude regions; (3) combined with the anomalous anticyclone over the Indian Peninsula and the anomalous cyclone over central Asia, which formed the two-step transport of water vapor, the water vapor from the Arabian Sea could be transported to central Asia and northern Xinjiang. Partial correlation analysis indicated that thermal anomalies over the Tibetan Plateau largely affect circulations in the middle and high troposphere and the second step of water vapor transport, while the thermal anomalies over northwestern Plateau mainly influence the first step of water vapor transport.