To investigate the vibration effect of the drainage tunnel blasting on the lining structure of the adjacent existing tunnel, the drainage tunnel construction of Beishan No.2 Tunnel in Hao-Ji Railway was considered as the research background. Field monitoring and of dynamic finite element methods were used to analyze the variation laws of peak vibration velocity and stress of the exiting tunnel lining due to the drainage tunnel blasting. The results showed that under the existing blasting scheme, both on-site monitoring and numerical simulation indicated that almost all the peak vibration velocities of tunnel lining were much greater than the allowed vibration velocity of 5 cm/s. The maximum tensile stress was larger than the ultimate tensile strength of the lining concrete, resulting in cracks in the lining; and the blasting of the drainage tunnel has the greatest impact on the side wall of the tunnel facing the vibration source, with a maximum peak vibration velocity of 17.98 cm/s, significantly exceeding the allowed vibration velocity. Based on the Sadovsky's formula fitted from field monitoring data, the maximum charge amount per delay was calculated, and an optimized blasting scheme for the drainage tunnel was proposed. Numerical simulations and on-site monitoring confirmed that the peak vibration velocity of the optimized blasting scheme did not exceed the allowed vibration velocity, thereby ensuring the safety of the tunnel's main lining structure.