Remote sensing of water vapor amount along the slant path (SWV: Slantpath Water Vapor) using the groundbased GPS is the basis of getting the threedimensional distribution (water vapor tomography) of water vapor on the immediate vicinity of the site. Many estimation methods have been developed in recent year, but more or less there are problems that hindered these method from putting into operational use, such as nonrealtime resolving, low accuracy resolving result, or complex convert formula. By running the Bernese (version 5.0) doubledifference processing script and the zerodifference processing script respectively, the key elements of noisotropic component of water vapor in different azimuths above the GPS receiver, the wet gradient, and zerodifferenced residuals are calculated. Then slant path water vapor amount can be accurately retrieved. In order to prove the accuracy of this new method, the observation data of a comparative observation experiment of slantpath water vapor between groundbased GPS and microwave radiometer conducted in summer 2007 are recalculated. Comparison between GPS and MR shows that RMS is less than 4 mm, which means that the estimates of SWV can be used to retrieve the three dimensional information of water vapor.