Abstract: In existing Global Navigation Satellite System (GNSS) water vapor tomographic techniques, only signals which penetrate the entire research area are used. Due to the specific geometric distribution of satellite constellations and receivers as well as the specificity of tomography area, many signals penetrating from the side of a research area are excluded as ineffective information, which undermines the tomographic result. To solve this issue, a method is proposed for improving the utilization of signal rays by adding an assisted tomographic area, which allows the signal information crossed from the side of a research area to be utilized as well. An experiment using data from the Continuously Operation Reference Stations (CORS) network of Texas in UAS, is compared with radiosonde data of 72 249. The results show that the proposed method can enhance the accuracy of tomographic results, the improvement rate of Root Mean Square Error (RMS) was 14.6%.