Based on precipitable water vapor received from groundbased GPS，data of dense surface automatical meteorological stations，and conventional sounding data in Shijiazhuang on August 2010，this paper studied the evolution tendency of GPS precipitable water vapor and potential pseudoequivalent temperature during a heavy rain induced by the advance and retreat of the west Pacific subtropical high.The results show:(1)Rainfall usually occurs when the GPS precipitable water vapor is higher than the average value，especially near its maximum value.The heavy rain period is corresponding to the maximum stage of GPS precipitable water vapor.Upperlevel trough is helpful to the occurrence of the convective heavy precipitation at the late period of GPS precipitable water vapor increasing.Weak precipitation will continue at the early period of GPS precipitable water vapor decreasing.(2)In the stability precipitation process，the GPS precipitable water vapor shows a multipeak wave shape，and its amplitude is relatively small.The heavy rain period is corresponding to the maximum stage of GPS precipitable water vapor.In the convective precipitation process，the GPS precipitable water vapor changes dramatically，and the peaks of GPS precipitable water vapor and actual precipitation are exactly corresponding.(3)Rainfall easily occurs when the deviation coefficient of GPS precipitable water vapor is positive，and the heavy rainfall generally happens while the deviation coefficient is higher than one.The deviation coefficient of convective thunderstorm or shower is slightly smaller than that of stability precipitation.(4)The prophase highenergy accumulation is a necessary condition of rainfall.The rainfall of subtropical high usually occurs in the rapid decline phase of potential pseudoequivalent temperature or its valley areas.The precipitation will be stronger when the potential pseudoequivalent temperature is at higher peak with more sharp movement and longer duration of high value.