［Objective］The construction disturbance caused by newly built stations with large-section rectangular interchange passage closely under-passing existing urban rail transit stations (hereinafter referred to as ′existing stations′) is significant, and there is a lack of relevant research on this topic. It is necessary to investigate the deformation and disturbance situation on the existing station caused by the newly built station closely under-passing.［Method］Based on the theory of conventional random media and its algorithm, an improved algorithm is proposed. Taking Jinfu Interchange Station of Chengdu Rail Transit as an example, relevant engineering calculation parameters are selected, and a three-dimensional numerical simulation model for the interchange station is established. The mechanical response of Chengdu Rail Transit Line 27 newly built Jinfu Station interchange passage closely under-passing existing Line 6 station is analyzed. The precision of improved algorithm and simulation model is verified through measured and simulated value comparison, and a sensitivity analysis of parameters is carried out.［Result & Conclusion］Through comparing measured and simulated values, the feasibility of the improved algorithm and simulation model mentioned above is verified. Constrained by the supporting piles, a bending moment or ′groove′ phenomenon appears on the structural base plate at the existing station. Additionally, with the increase of net spacing between the new interchange passage and the existing station, the most unfavorable part on the structural base plate shifts outward from the tunnel centerline. As the foundation reaction coefficient increases, the interaction between soil and the existing station intensifies, resulting in significant deformation, bending moment, and shear force on the structural base plate of existing station.