A running tunnel on line 6 of Beijing Metro undercrosses Dongsi Station of line 5 of Beijing Metro with zero clearance. During the construction of the running tunnel, numerical simulations are made, field monitoring is conducted, and the construction scheme is optimized. The influence of the construction of the running tunnel on the existing structure is summarized. Conclusions drawn are as follows: 1) Fullface grouting can improve the strength of the soil to be tunneled through, which in turn reduces the settlement of the existing Metro station; 2) The jacks installed can provide support to the floor of the existing Metro station, which guarantees the maximum settlement of existing structure to be within 3 mm. 