Abstract: When the lateral grouting method is used to control the transverse elliptic deformation of a shield tunnel, the additional earth pressure around the shield tunnel and the deformation characteristics of the tunnel are not clear. The effects of side grouting on the existing shield tunnel are studied through the shrinkage model tests with the geometric similarity ratio of 1∶10. The test results show that under the action of grouting extrusion, when the soil pressure around the tunnel increases locally at the grouting point, both sides decrease to a certain extent, resulting in an obvious horizontal passive soil arching phenomenon. Under the influences of additional grouting loads, the vertical elliptic deformation occurs near the grouting point, while the transverse elliptic deformation occurs farther away from the grouting point, and the tunnel has reverse bending phenomenon. In the process of grouting, the diffusion mode of "penetration→compaction→splitting" and the diffusion mode of "compaction→splitting→penetration" occurr, and the diffusion mechanism of the two grouting diffusion modes is clarified. The additional loads on the outer wall of the tunnel are mainly formed by the grouting pressure through osmotic diffusion and splitting diffusion. Meanwhile, the grout compresses the soil deformation of the grout to a certain extent on the grout around the tunnel.