The in-situ stress is one of important basic data for stability evaluation, engineering design and construction of tunnels. For southwest high mountain region, the in-situ stress in the site test is very difficult. Thus, for satisfying engineering design and construction, it is necessary to back analyze the in-situ stress. The highway tunnel which locates at the 1# road of Lianghekou hydropower station is researched as the object. Based on measured displacements, the inversion model of initial earth stress is built. By comparing the calculated and measured results, the reasonable horizontal pressure parameters and the modulus of elasticity are confirmed.