In order to study the deformation law and its influencing factors when the shield tunnel underpasses the high railway foundation, a three-dimensional numerical model is established based on the actual project in Xi'an city, and the variation laws of the displacement of the high railway foundation and the displacement of the track bed when the shield tunnel underpasses the existing high railway foundation are analyzed. At the same time, orthogonal experiments are used to study the influences of tunnel excavation distance, tunnel underpass angle and other factors on the high railway foundation. The results show that the maximum vertical displacements of roadbed and roadbed after shield tunnel construction are 9.18 mm and 7.43 mm, respectively. The maximum lateral displacements of subgrade soil in different directions are 0.24 mm and -0.29 mm, respectively. The maximum displacements of the track bed in different directions are 0.17 mm and -0.13 mm, respectively. In addition, the vertical clear distance has the greatest effect on the vertical deformations of the existing high railway foundation and the high railway foundation bed. The underpass angle has the greatest influence on the transverse deformation of the existing high railway foundation bed.