Abstract: At present, the theoretical research on the deformation of adjacent tunnels with small curvature radius induced by excavation in soft soil generally regards the foundation as a linear elastic body, without considering the influence of soil rheological characteristics, and seldom analyses the deformation characteristics of curved tunnels, so it is impossible to accurately predict the influence of excavation on the deformation of existing tunnels with small curvature radius under time effect. Firstly, a mechanical model for the deformation of the adjacent existing tunnel with small curvature radius induced by the excavation of the fractional order Merchant viscoelastic soft soil foundation pit is established, and the Laplace domain parameters of the fractional order Merchant viscoelastic soft soil are derived according to the Laplace time-domain variation characteristics. Secondly, based on the theory of foundation pit unloading and Mindlin stress solution, the additional stress field on the adjacent existing tunnel with small curvature radius is solved. According to the theory of Pasternak foundation and Timoshenko beam, the radial and vertical deformation time-domain solutions of the existing tunnel with small curvature radius are derived by finite difference method and Laplace forward and inverse transformation. Finally, the measured data and 3D numerical simulation results are compared with the analytical solution, and good consistency is obtained.