Abstract: The impact of starting of tunnel boring machine (TBM) on the deformation of the existing shield tunnels under loads during the construction process of connecting passage by the shield tunneling method is currently unclear. By designing a 1:10 scaled model experiment, the experimental researches on the impact of starting of the TBM on the existing shield tunnels are conducted. The results indicate that, during the construction of connecting passage by the shield tunneling method, under the action of the top pushing reaction force of the TBM, the existing shield tunnels at the starting end undergo horizontal elliptical deformation within a range of about 1 tunnel diameter at the position of connecting passage, while the vertical one occurs at both ends. When a shield tunnel undergoes cross-sectional deformation, the deformation of horizontal diameter is about 3~4 times that of the vertical one. The horizontal bending deformation occurs in the direction of upward pushing reaction force within a range of approximately 1 tunnel diameter at the location of the connecting passage, and the horizontal bending phenomenon occurs on its both sides. The trend of the vertical deflection deformation is the same as that of the horizontal one, and its amplitude is smaller than that of the horizontal deflection deformation. The increase in the horizontal diameter within the range of about 1 times the tunnel diameter at the location of the connecting passage leads to an increase in the horizontal soil pressures at both sides of the tunnel, while the decrease in the vertical diameter leads to a decrease in the vertical soil pressures at both the top and bottom of the tunnel. The variation of soil pressures around the shield tunnel are the result of the combined action of cross-sectional deformation and longitudinal deflection deformation of the shield tunnel. It is recommended to consider both the cross-sectional deformation and the longitudinal deflection deformation in the stress analysis process of the shield tunnel.