Abstract: The NCEP/NCAR Reanalysis 1 datasets including global precipitable water data since 1948 have been widely applied around the world,which have provided homogenously spatial and temporal distributed data for global and regional water vapor study.As a new method to estimate water vapor,ground-based GPS measurements have been developed in recent years.The GPS/Meteorology sites in Southwest China (Sichuan,Chongqing,Yunnan,Guizhou) have provided regional precipitable water estimates 24hrs per day since 2007.Based on the analysis on the fundamental differences of their algorithms and temporal and spatial coverage and so on,this paper compares precipitable water values from GPS measurements and NCEP R1 in Southwest China.The analysis shows that the two datasets could show consistent characteristics of distribution and seasonal variation of precipitable water in Southwest China.Both GPS measurements and NCEP R1 could show the spatial-temporal characteristics and variation of regional water vapor.Meanwhile,precipitable water values from GPS measurements and NCEP R1 are linearly correlated and similar.Besides,quantitative differences between precipitable water values from NCEP R1 and GPS measurements are found as well.