The rapid development of metro construction will inevitably cause the metro line and the existing bridge pile foundation cross engineering conflicts, in order to ensure the safety of the viaduct and the simultaneous completion of the construction of the metro tunnel, the viaduct needs to be pile foundation replacement. In this paper, Guiyang city rail transit line 3 Huaguoyuan West Station ~ Huaguoyuan East Station interval tunnel under Guihuang Road viaduct as the research object, the use of finite element software on the whole process of pile foundation replacement and tunnel construction through the process of numerical simulation, and with the on-site monitoring data compared to analyse and validate the accuracy of the results of the numerical simulation, and to study the replacement process of the bridge deformation and the change rule of the pile foundation force. The results show that: using passive replacement technology and replacement bearing platform as the bearing structure of the bridge for pile replacement, the bridge superstructure load can be effectively transferred to the replacement system after the existing pile truncation, the abutment is firstly uplifted and then settled and then tends to be stable, the bridge deformation and the replacement system force are within the safety range, the replacement pile force and settlement is not uniform; the tunnel construction crossing did not have too much influence on the new replacement system, the pile foundation replacement programme has no impact on the new system, and it has a great influence on the new system, and it has a great influence on the new system. The tunnel construction crossing does not affect the new replacement system too much, the pile foundation replacement scheme is safe and feasible.