Abstract: In the simultaneous adjustment of Astro-geodetic network 1980 and China National GPS geodetic control network 2000,in order to reduce the geodetic observation data to the ellipsoid of WGS84,the technique of remove-restore and Earth gravity model is adopted to refined calculate the deflection of the vertical of 48 919 geodetic point in WGS84,by using the gravity data and 30″×30″ DEM in whole country.And the observation deflection of the vertical of 115 astronomic points in WGS84 is used to the exterior precision check.The total accuracy of the deflection of the vertical in a north-south direction is 1.45″,and that in a east-west direction is 1.50″.The result has been already used in the simultaneous adjustment of two geodetic networks.