On the background of Yuzhou tunnel at the airport road of Chongqing， it is one small spacing tunnel with serious bias. On` the basis of engineering geology， choose the tunnel section with bias most serious and then build the ANSYS finite element model to simulate the process of broaden. Analyse the surrounding rock displacement， stress strain and plastic zone when the tunnel is broaden or not. Conclusion that in the process of tunnel broading， the displacement of surrounding rock dome downward is big; In addition， as the influence of bias from the surrounding rock above the central rock pillars and right tunnel side wall bears big compressive stress and produces soil plastic deformation. Finally， suggest strengthening the support on the two area above-mentioned in the process of construction.