By using the WRF model, groundbased GPS data, and conventional observational data, combining with the high spatialresolution (10 km) WRF model output data and high timeresolution (30 min) GPSPrecipitable Water Vapor (GPSPWV) data, a heavy precipitation process in the Sichuan basin is synthetically analyzed, especially on the vapor variation characteristics and the relationship between various physical quantities and GPSPWV data. The results show the heavy precipitation event was caused by the interaction of the plateau vortex and the southwest vortex, and the WRF model can simulate the rainfall area and intensity well. The increase and decrease trends of atmospheric precipitable water vapor simulated by WRF fit with GPSPWV. The vertical distribution of water vapor density reflected the distribution of precipitable water vapor, and the water vapor density decreased while the height increased. At the beginning of the precipitation, the water vapor density decreased quickly while the height increased. At the strong stage of the precipitation, the water vapor density decreased slowly while the height increased. The water vapor convergence resulted in the increasing of water vapor density and precipitable water vapor. The change of the divergence term of the wind agreed with the vapor flux divergence. The advection term of the water vapor had less contribution to the water vapor flux convergence. The convergence of the water vapor was mainly caused by the convergence of the wind field.