Qiansanmen tunnel of Beijing Underground Rail Transit Line crosses above existing Metro connection gallery and existing power tunnel. The design scheme of “isolating pile protection and sequence excavation” is proposed for the tunnel. The sequence excavation of the tunnel is simulated, and the displacement of the existing Metro connection gallery during tunnel construction is calculated, so as to guarantee the safety of the existing structures in the urban area. Conclusions drawn are as follows: The scheme of isolating pile protection and sequence excavation adopted is feasible and that the safety of the existing Metro connection gallery and the existing power tunnel can be guaranteed.