The technique of ground-based GPS tomography is a newly spatial tool to sense the water vapor profile in atmosphere area. It has become a complementary technique for other conventional atmospheric sounding techniques. In this study, the radiosonde data was utilized to improve the accuracy of GPS tomography by forming the vertical constraint information. The experiment of Xi'an area tomography campaign was employed to assess the performance. The result shows that approach of fusion of radiosonde and GPS data for water vapor tomography can improve the accuracy of wet reflectivity, increase utilization of radiosonde data.