Abstract: Because it is affected by water pressure, lining leakage tends to occur in the core region of a karst cave. In order to solve this problem, a water diversion tunnel was constructed at the top of a main tunnel to drain karst water in order to reduce the water pressure around the tunnel lining. Based on construction of a water diversion tunnel for a railway tunnel in western China, this paper shows that the blasting vibration velocity and the structural stress were acceptable and the tunnel structure had basically no deformation and a relatively stable structural stress based on the monitoring of the water diversion tunnel blasting vibration velocity, structural stress and deformation of the main tunnel lining. The monitoring data indicate that construction of the water diversion tunnel had little influence on the main tunnel lining structure, which ensured the stability of the tunnel structure and operation safety of the railway.