The use of underground structures such as tunnel for subways, highways, material storage, and sewage and water transport is increasing in the West of China. As the strongest earthquake recent years，the Wenchuan Earthquake (M8.0) on May 12nd, 2008，has caused very severe casualties and property losses. Relying on the left line tunnel portal segment of the Xiaoshicun Tunnel, the dynamic response analysis were conducted by FEM. The response patterns of stressand displacement of the tunnel structure were respectively studied both under the single horizontal earthquake action and the interaction of horizontal and vertical earthquake actions. The results indicated that the difference of seismic response in diffrent parts of tunnel linging was obvious, the response under both horizontal and vertical earthquake action was bigger than that under single horizontal motion.