The unloading of foundation pit excavation would affect the lower metro shield tunnel in waterrich and sandygravel strata. As a result, the deformation rules of the shield tunnel are studied in terms of reducing the influencing degree of unloading of foundation pit excavation on lower metro tunnel and increasing longitudinal stiffness of tunnel. The uneven longitudinal deformation of the tunnel is reduced by setting prestressed anchor rope in tunnel, setting hidden beam in the road bed and composited with segment and longitudinal fixing the Usteel. Meanwhile, the top beam is formed by advanced support of pipe curtain. The basic principle of vertical stratification, longitudinal segmentation and excavation after support is adopted for foundation pit excavation. The results show that the deformation of the tunnel has been effectively controlled and the normal operation of the metro has been guaranteed. 