Abstract: In order to study the stress transfer mechanism of pile foundation during underpinning and the influence of tunnel excavation on pile foundation group, a numerical simulation of pile foundation underpinning and metro tunnel construction was conducted by FLAC3D based on the shield tunnel of Shenzhen metro line 10 passing through the bridge pile foundation of Guangzhou-Shenzhen motorway. The results show that the bridge load system changes from the order of bridge deck→pile foundation-soil to the order of bridge deck→existing pile foundation→underpinning pile→subsoil after underpinning of pile foundation, and the overlying load on underpinned pile is effectively transferred to the new pile; the settlement deformation induced by underpinning and excavation can increase the resistance at pile end and pile friction, so the maximum principal stress of pile foundation is reduced; the settlement of bridge pile foundation is mainly the deformation induced by ground loss and excavation disturbance in the process of shield tunnelling, and the proportion of settlement caused by underpinning of pile foundation is 20%-30% of total settlement; the reduction effects of settlement deformation, lateral displacement and principal stress of pile founda? tion occur at the underpinned pile while there is little change for the non-underpinned pile; deformation of lining structure of shield tunnel mostly occurs at the area near the underpinned area and it is mainly of settlement with small lateral deformation.