GPS-PWV from Jiangsu ground-based GPS water vapor monitoring system was used to analyze a severe convective weather process happened in summer of 2009 in Jiangsu province, as well as the variation of GPS-PWV at each period and the characteristics of water vapor transportation. Numerical simulation of this process with WRF model shows GPS-PWV is quite sensitive and timely reflects the water vapor change. Results of numerical simulation analysis based on WRF model suggests that the strong convective storm is caused by the interaction of strong vapor and convergence ascending motion, weak cold air activities at middle levels, the strengthening southwest low-level jet and the weakening stability of convection layer, etc. The precise variation of water vapor provided by GPS-PWV and the thermal and dynamic condition simulated by numerical simulation can be combined to forecast the strong convective storm and precipitation areas well.