To study the influence of foundation pit excavation on the deformation of existing metro tunnel，the finite element method considering the small strain of soil was adopted to simulate the excavation process. The influence of vertical excavation unloading on the deformation of the underlying tunnels was studied. Besides，the deformation characteristics and the influenced zone of the tunnels were analyzed with different excavation depths. The controlling effects of different soil reinforcement measures on tunnel deformation were compared. The results show that the vertical unloading mainly causes the vertical deformation of tunnels，with the decrease of the excavation depth，the vertical deformation of tunnel and the influenced zone are decreased. It is suggested that the entire basal soil reinforcement selected for the soil reinforcement of foundation pit in horizontal plane， and the back tail reinforcement is selected in vertical plane. The proper strength of soil reinforcement for foundation pit is between 0.5 and 1.5 MPa.