Abstract: Based on the monthly reanalysis data from 1961 to 2012 provided by the European center, the characteristics of water vapor andits transport over southwest China are analyzed. The analysis results indicate that the water vapor content of southwest China had been decreasedin the 50 years. The water vapor between 850 -700 hPa is more abundant than other layers. There is more water vapor content in eastof southwest China and less in west. The water vapor is mainly from four channels: In spring, the water vapor comes from the Bay of Bengleand westerly. In summer, the water vapor comes from the Bay of Bengle and Indian Ocean. In autumn, the water vapor comes from the westPacific Ocean. In winter, the water vapor comes from westerly and the west Pacific Ocean. Most part of southwest China is water vapor convergence.There are two water vapor convergence centers, One locates in the border of Tibet and Sichuan, and the other in Guizhou and surroundingareas. Most part of Yunnan is water vapor divergence, except in summer.