Based on the observational data from the groundbased GPS (Global Positioning System) network in Chengdu Plain, the Precipitable Water Vapor (PWV) in the atmosphere is calculated. The Vertical Integrated Liquid water content (VIL) is derived from the Doppler radar detection data. Analysis is made of the variation characteristics of water vapor during weather modification operations by means of those new detection data. The relationship between GPS PWV and rainfall after weather modification operation is obtained preliminarily. The results show that there is a good corresponding relation between GPS PWV and artificial precipitation enhancement; GPS PWV decreases with the increasing rainfall intensity in 1 to 3 hours after the weather modification operation, which reflects that catalysts lead the partial supersaturated vapor over ice layer to convert into precipitation. GPS PWV, in combination with VIL detected by a new generation of Doppler radar, has good application prospects in weather modification operations and shortterm weather forecasting and nowcasting.