In order to study the impact of double-line shield tunnel underpass construction on the structural deformation of viaducts, a numerical model is established by using finite element software Midas GTS to simulate the whole process of double-line shield tunnel construction based on the viaduct project of Zhengxu municipal railway under Xinzheng airport T1 Terminal. By comparing the numerical simulation results with the on-site monitoring data, the reliability of the model is verified, and the deformation development law of the viaduct and its conformity with the engineering code control standard are analyzed. The results show that the deformation characteristics of viaduct piers and abutments are significantly affected by the relative position of the left and right line tunnels and the construction progress. After the double-track tunnel is completed, the maximum settlement of ZQ11a pier is 2.265mm , the maximum settlement difference between longitudinal adjacent piers ZQ08a and ZQ09a is 0.963mm , the maximum settlement difference between transverse adjacent piers and abutments ZQ08a and ZQ08b is 1.487mm , and the maximum horizontal displacement of ZQ08a is 0.792mm . All deformation indicators meet the requirements of the specification control standards, which can ensure the normal operation of the viaduct of the passenger drop-off platform in Terminal 1. The results deepen the understanding and awareness of the underpass construction process of double-line shield tunnels, and can provide references for the construction and safety management of similar tunnel projects.