Abstract：We studied the method of computing the horizontal tectonic stress field by the earth gravity field, and then the horizontal tectonic stress field in western Sichuan is computed with the EGM2008. The results show that we can quickly obtain the tectonic stress field using gravity field data. The horizontal tectonic of the Longmenshan and Xianshuihe-Anninghe fault zones is greater, and the accumulation degree is higher than any other area, which reflects that tectonic movement is more active in these areas. The horizontal tectonic stress from the Bayanhar block to the southern China block to the Sichuan-Yunnan block shows clockwise rotation. In the Bayanhar block and southern China block boundary, the strong stop of Sichuan basin in the south China block results in the formation of Longmenshan foreland thrust zone. The tectonic stress field gradually decreases with the increase of depth, and the frequency of seismic activity decreases accordingly. The tectonic stress field is densely distributed with active tectonic activity and frequent seismic activity, which indicates that there is a corresponding relationship between seismic activity and tectonic stress accumulation.