Relying on the Guangzhou Metro Line 8 shield tunnel side-crossing the Huanan Express Viaduct pile project, and considering the situation of bridge piles with and without isolation piles, the finite element numerical model was established to study the ground settlement before and after reinforcement, the changes in additional axial force and bending moment of bridge piles, and the pile displacement. Then reinforcement optimization design was carried out. The results show that the isolation piles can effectively reduce the pile top displacement of existing bridge piles perpendicular to the driving direction. Due to the traction effect of the isolation piles, there is basically no reduction in the displacement of the middle of the bridge piles, and even a very small increase in the horizontal displacement. The isolation piles, which have a certain shielding effect on existing bridge piles, basically eliminate the horizontal displacement of bridge piles parallel to the driving direction. The isolation piles greatly reduce the additional axial force of the bridge piles, greatly reduce the additional bending moment of the bridge piles in the vertical shield direction, and basically have no effect on the additional bending moment in the parallel shield direction. Properly increasing the diameter of the isolation pile and the distance between the isolation pile and the bridge pile can effectively reduce ground settlement. It is recommended to set the isolation piles within 6 to 8 m away from the tunnel, so as to meet the safety net distance required by the specification and to protect the existing bridge piles to a greater extent.