Abstract: We study the ground-based GPS zenith water vapor remotely sensing theory,and propose the double difference method for ZTD estimation with IGS precise ephemeris provided and precision clock error.We use a Kalman filtering method and a double-difference method to estimate the ZPD,respectively.We compare the results with zenith delay provided by IGS stations.The results calculated with two methods and provided by the IGS trend of the same epoch with the largest difference doesn’t exceed 2 cm.According to the solution of ZTD,we use empirical models to solve ZHD,and isolate ZWD.Finally,we carry out the solution of sub-atmospheric precipitation.