The study of influence of Metro construction on existing structures is very important. Numerical simulation is made on portioning excavation and structural backfilling of access section of Xi’an Metro Line No. 6 crossing above existing shield tunnels. The influence of unloading and reloading induced by open cut construction of the access section on lower shield tunnels is studied. The calculation results show that: 1) The influence of unloading and reloading induced by open cut construction of the access section on surrounding soils is obvious; the soils tend to uplifting and the maximum uplifting occurs to foundation pit base for about 48.15 mm. 2) The maximum uplifting of lower right line shield tunnel is 10.86 mm; and the differential deformation of structure is 0.008 9%. 3) The maximum tensile strength and compressive strength of tunnel segment are 2.13 MPa and 4.92 MPa respectively. The results show that the deformations and stresses of the tunnels can meet the safety requirements.