A shieldbored running tunnel of Line 2 of Shenyang Metro passes underneath the piles of an existing pedestrian bridge, and some of the piles have to be cut. In the paper, 3D numerical simulation is established and analysis is made on the loadbearing capacity and structural deformation of the segment structure after the piles are cut; and accordingly the design is optimized and countermeasures, such as temporary support for the piles of the existing pedestrian bridge installed before the shield reaches, optimizing the shield boring parameters during boring, and simultaneous grouting and secondary reinforcing grouting, are taken. The monitoring shows that the pedestrian bridge keeps stable and the countermeasures taken are effective.