No. 2 Sizhai tunnel on GuiyangGuangzhou railway crosses underneath the existing Ruipo tunnel on XiamenChengdu expressway with a small angle. Theoretical analysis, numerical simulation and site monitoring are made to achieve a safe and economic design of the tunnel. Main study contents and conclusions drawn are as follows: 1) No. 2 Sizhai tunnel, which crosses underneath the existing tunnel with a small angle, is located in fractured rock mass, therefore the scope of the influence induced by the construction of No. 2 Sizhai tunnel is large. The influence scope can be analysed by means of Peck formula. 2) The settlement control standard of the existing tunnel can be defined on the prerequisite that the structural safety of the existing tunnel is guaranteed. 3) The preliminary design of the tunnel can be verified by means of numerical simulation, and therefore the construction methods and countermeasures can be optimized.