Excavation of foundation pits adjacent to operating shield tunnels is prone to induce pipe ring deformation and even excessive ellipticity. The outer-ring micro-perturbation grouting technology provides new ideas for the recovery of tunnel deformation. Model test verification and numerical simulation extension were adopted in this study. First, indoor model tests were conducted to verify the recovery effect of grouting volume on tunnel ellipticity. On this basis, a three-dimensional fine simulation model was established to further analyze the impact of grouting parameters and the spatial position relationship between the tunnel-foundation pit on the force deformation of the tunnel pipe ring. The results show that: 1) In the model test, the ellipticity of the shield tunnel pipe ring structure is restored from 0.35‰ to 0.03‰ after outer-ring grouting, which verifies the effectiveness of grouting correction. In numerical simulation, when the horizontal distance between the tunnel and the foundation pit is 18 m and the depth of the tunnel is -15 m, the ellipticity of the pipe ring structure is restored from 8.37‰ to 0.20‰, confirming the significant recovery effect of outer-ring grouting on tunnel deformation. 2) When the grouting amount is 4 m3, the maximum diameter difference of the pipe ring is 4.070 mm. The recovery effect is remarkable, but the degree of unilateral uneven deformation is high. The grouting length is increased to 3 m, the maximum diameter difference of the pipe ring is reduced to 3.559 mm, and the uneven deformation is significantly reduced. Under the working conditions of this study, the grouting amount of 4 m3 and the grouting length of 3 m are the preferred solutions for out-of-ring grouting. 3) When the tunnel is located below the excavation surface and the horizontal distance exceeds 18 m, the tunnel exhibits excessive deformation after grouting. It is recommended to reduce the amount of grouting or increase the length of grouting under such conditions to avoid excessive correction and disease. 4) The calculation of the maximum diameter difference of the pipe ring is simple and can significantly reflect the degree of uneven deformation of the tunnel, which can be prioritized as an evaluation index in the actual grouting construction.