Geological description and joint statistic were done on a tunnel construction. By analyzing the distributing regularity of joint growth with stereographic projection method, the rock mass structure model was built. According to this model, the stability of surrounding rock was calculated with distinct element method and the broken modes were analyzed on the tunnel. Meanwhile, the supporting manner and mechanics mechanism by steel bar combining with rock bolt were analyzed. On the basis of the measuring press burdened by the steel bar and the convergence of the tunnel, the stability of the surrounding rock and the support system were analyzed, and the primary causations for construction accidents in tunnel were summarized. Finally, feasible suggestions for supporting were given.