Using the daily NCEP/ NCAR reanalysis data (2.5°×2.5°lat/lon) in 2008 and dai ly rainfall data of 29 meteorological stations from January to February between 1970 and 2008 in the southern Xinjiang Basin， the variation of atmospheric circ ulation circumstances, water vapor source, water vapor transfer and the effect o f low level jet were analyzed. The results showed that the distribution of the precipitable water field was different from the vector field of water vapor flux . In the water vapor transfer, the contribution of Beihai was the most, w ith water vapor transfer in middle and lower layers by west and east routes, res pectively. Both water vapor transfers of the west route and east route were changed into th at of southwest airflows in the westside of the Tibetan Plateau, with vapor tran sfer in 700 hPa obviously more than 500 hPa, thus the low level jet plays an imp o rtant role in the long distance transportation of water vapor to the southern X injiang Basin.