In order to study the settlement of the existing subway tunnel below caused by road construction, on the basis of the construction road diagonally above the subway tunnel, a field tunnel settlement deformation measurement study was conducted to analyze the settlement curve of the subway tunnel in the roadbed grouting reinforcement, roadbed and pavement structure layer construction stages. A subway tunnel-soil-road model was established to simulate the slurry reinforcement process of road construction and the construction of roadbed and pavement structure layer, and the accuracy of the refined model was verified by comparing the calculated results of underpass tunnel settlement with the actual measured values on site. Based on this, the influence law of key parameters such as the total construction thickness of roadbed and pavement structure layer, the nature of road soil, the submerged soil layer of tunnel, and the strength of tunnel lining on the settlement of the subway tunnel was analyzed. The results show these as follows. the settlement value of the subway tunnel is positively correlated with the construction thickness. The presence of the road has less influence on the settlement of the tunnel, and its elastic modulus and Poisson's ratio have almost no influence on the settlement of the subway tunnel. The larger the elastic modulus of the lying soil layer, the less deformable the soil layer is, and the smaller the settlement of the subway tunnel is, the increase in the elastic modulus of the lining has less influence on the settlement of the subway tunnel instead.