Abstract: In the paper, the mechanical behaviour of a metro tunnel construction adjacent to existing pile foundation in Shenzhen is studied with 3D FEM numerical simulation method. Comparing with the case of no pile foundation,the disadvantageous distribution of deformation and internal forces in the tunnel structure are demonstrated,particularly in its side wall adjacent to the existing pile foundation. In addition, the tunnel construction results in also the tensile deformation in the existing pile foundation. Therefore, it is necessary to take some reinforcing measures to guarantee safety of the tunnel itself and the adjacent existing pile foundation. Finally, based on analysis of deformation using different stiffness reduction coefficients, it is found that the tensile deformation values hardly change,because different assembling patterns of tunnel lining segments have little effects on the adjacent existing pile foundations.