Abstract: Based on the engineering background of adding a drainage tunnel section during the overhaul of the Songshuwan Tunnel, two construction schemes were proposed to connect the channel and the intersection section of the drainage tunnel.Numerical simulation methods were used to verify the effectiveness of the finite element model by comparing it with on-site monitoring data.The deformation characteristics of the lining and steel arch under the two construction methods were analyzed.The results indicate that: 1) both circular arc smooth connection and right angle connection can ensure the safety of lining deformation and stress; 2) When a right angle connection is adopted, the lining may experience stress concentration due to unfavorable spatial geometric characteristics.On the other hand, using a smooth circular arc connection can avoid adverse features such as edges in space, making it more advantageous; 3) The most unfavorable section during the construction of the transition section is the common section connecting the turning section with the connecting channel and drainage hole; 4) Through the comparison of the deformation and stress state of the tunnel lining under the two construction methods, it is suggested to adopt the circular arc smooth transition in the field construction of the connection channel and the drainage tunnel.