Abstract：The current research situation and commonly used method of stability for excavation and lining of large-span tailrace bifurcation tunnel at home and aboard are reviewed. Based on summary studies，an evaluation method to analyze the stability of excavation and lining structure is proposed. It involves the basic principles of numerical method，analytical contents，flow charts and evaluation index. By employing this evaluation method，the tailrace bifurcation tunnel of Xiluodu hydropower station is analyzed，including the distribution characters of deformation，stress and yield zone in the surrounding excavated rock mass and the reinforcing effect under different stress releasing conditions. The deformation and stress state in surrounding rock mass and lining structure also are investigated under operation and maintenance loading conditions. The numerical results and monitoring results are consistent. Based on the numerical results of practical projects，it shows that the proposed evaluation method related to tailrace bifurcation tunnels can be applied to the design and construction of the similar projects.
