Abstract: Based on the dislocations of earthquake faults, the geostress measurement and GPS regional displacements, this paper aims to explore the variation of geostress in the Longmenshan mountainous area before and after the 2008 Wenchuan earthquake using numerical inversion analysis method. The results of numerical simulation demonstrate that the average tectonic goestress in the Longmenshan mountainous area ranged from 12.6 MPa to 12.8 MPa before the Wenchuan earthquake. The direction of maximum principal stress ranges from NW to NEE.An clear change of geostress had been caused by the Wenchuan earthquake. It behaves mutation effect, hanging wall and footwall effect, and distance effect. The tectonic geostress of the hanging wall of the earthquake faults reached an average of 11.30MPa, whereas the geostress of the footwall at an average of 6.50 MPa. Meanwhile, the direction of maximum principal stress ranged from NWW to NEE.The geostress had clear mutation characteristics, which appeared to be the release or local increase of the geostress. Especially the geostress was released obviously at the foot wall. Different degree of geostress releases or locally rises at the hanging wall. With the increase of distance to the earthquake faults, the mutation effect of the geostress was gradually weakened.