In order to study the influence of a shield tunnel oblique underpass construction on the existing expressway project, taking the shield tunneling project of an urban rail transit as the background, three dimensional numerical analysis of shield construction was carried out by using FLAC3D. The influence of shield tunnel construction on road surface and cutting slope was studied, and the safety of construction scheme was evaluated. The results show that: the settlement of the road surface presents three-dimensional asymmetric characteristics when the shield is obliquely underpass. In the direction of cross section, the settlement curve presents a linear law of low left and high right, and in the longitudinal direction, the settlement curve presents an asymmetrical "V" shape with high left and low right. The settlement in the direction of cross section is always greater than that in the longitudinal direction. The vertical displacement of the slope is larger than the horizontal displacement, and the main deformation is settlement. When the horizontal distance between the shield excavation face and slope toe is about 2 times of the tunnel diameter, the slope displacement increases significantly, and this section is a strong excavation influence area. After the double line shield tunneling, the maximum settlement of the pavement is 3.15mm, the longitudinal settlement change rate is 0.0094%, and the maximum horizontal displacement of the slope is 1.2mm, all of them are less than the deformation control standard. Highway pavement and slope are in elastic state, no plastic zone appears. The shield underpass construction of this project has little impact on the existing expressway. The research results can provide reference for similar shield underpass projects.