Abstract: This study addresses the synergistic force issue of segment-steel-concrete composite beams (SSC com? posite beams) in metro station structures built by the large-section mechanical construction method. A three-dimensional refined numerical model of the SSC composite beam is established to investigate the effect of prestress on the load-bearing performance of the SSC composite beam. The accuracy of the numerical model is verified through experimental tests on SSC composite beams, followed by an analysis of the influence of prestress magnitude, steel strand cross-sectional area, and steel strand position on the load-bearing performance. The results indicate that the contribution of the steel strand connected between the segments to the ultimate load-bearing capacity of the SSC composite beam varies significantly under different loading conditions. Under negative bending moment conditions(where segments are in the tension zone), the ultimate load-bearing capacity increases by 47.2%, while under positive bending moment conditions (where segments are in the compression zone), it only increases by 3.3%. Under positive bending moment conditions, the effects of prestress magnitude, steel strand cross-sectional area, and steel strand position on the load-bearing performance of the SSC composite beam are relatively small. However, under negative bending moment conditions, adjusting the prestress magnitude, steel strand cross-sectional area, and steel strand position can optimize the load-bearing performance of the SSC composite beam, effectively enhancing its stiffness against deformation and load-bearing capacity.