From 26 to 28 June 2015, Central Asia vortex caused heavy rainfall in the north slope of Tianshan Mountain. Using conventional data, NCEP reanalysis data and 9 weather stations’ GPS precipitable water vapor (GPSPWV) observations from the groundbased GPS networks, this article did indepth analysis on the vapor features in this process. The results show that: (1) before precipitation, at 500 hPa, the water vapor of the Arabian Sea was transported to Central Asia vortex through the Tibetan Plateau, the vortex was obviously moistened; during precipitation, at 700 hPa, the eastward water vapor transport channel was established, which was from Bay of Bengal through the Sichuan Basin and Hexi Corridor, and the easterly airflow and the southerly (SE) airflow of vortex itself converged the vapor in the heavy rain area. So, the lower atmosphere rapidly moistened in the heavy rain area. (2) All stations GPSPWV experienced wetting process from one to three days, the water jumped once or twice before precipitation began caused by the deep low vortex, and GPS PWV jumped more than 5 mm·(4 h)-1. (3) Under the same water vapor transport and vapor convergence conditions, the stronger the GPSPWV at stations of arid areas surges, the stronger the rain intensity is. To a certain extent, the water vapor transport and convergence has certain corresponding relationship with GPSPWV surge. (4) In 4-5 h before the heavy rainfall in Urumqi caused by Central Asia vortex occurred the growth rate of GPSPWV reached more than 4 mm, and the peak value of GPSPWV was almost twice of climatic mean.