For the railway in operation period, the high-speed railway subgrade outside its subgrade with the new cantilever retaining wall and other new loads will inevitably produce a certain displacement deformation on the existing subgrade and affect the smoothness of the track. In this paper, based on the construction of the cantilever retaining wall subgrade section of the Nanchang-Jingdezhen-Huangshan railway, combined with the actual conditions, the finite element analysis platform (PLAXIS 3D) is used to establish a three-dimensional numerical analysis model, and the HSS model is adopted to analyze the influence of the new cantilever retaining wall embankment on the adjacent existing lines, and the causes of the disturbance are explained. The actual construction standard value is used to control, and high-pressure jet grouting pile and isolation pile are applied to solve the disturbance caused by the new line to the existing line. Then the control efficiency of various measures is evaluated, and the key control points that need to be focused on for the new embankment of the parallel line are put forward. The calculation results show that the scheme of “8 m high pressure jet grouting pile + 4 m isolation pile” can effectively reduce the deformation of adjacent existing lines. The research results can not only be directly applied to the railway project, but also to the new high-speed railway project in the future, providing construction experience.