To evaluate the longitudinal mechanical behavior and deformation response of rectangular prefabricated metro station structures, a practical engineering project was relied upon. Based on the principle of longitudinal deformation equivalence, implicit expressions for the longitudinal equivalent flexural stiffness and its efficiency factor were derived. Two-factor analysis of variance and nonlinear regression were applied to quantify the global flexural behavior and to reveal parameter coupling mechanisms. Mechanical responses character of the station structure were examined from four aspects: major axis length, minor axis length, segment ring width, and component thickness, with their coupling relationships to maximum stress distribution clarified. A ring joint influence coefficient was further introduced to refine the longitudinal equivalent continuum model. The results show that the neutral axis position and the efficiency factor of longitudinal equivalent flexural stiffness remain constant regardless of segment ring width variations. The bending moment direction has negligible influence, allowing simplified design checks. Both maximum tensile and compressive stresses decrease with increasing major and minor axis lengths. Tensile stress is more sensitive to minor axis changes, while compressive stress responds similarly to both axes. Increasing the minor axis length is prioritized for tensile stress control, whereas coordinated adjustment of both axes is recommended for compressive stress optimization. The sectional stress state is primarily governed by the bottom slab thickness, which should be prioritized for stress optimization in design. As the ring joint influence coefficient increases within [0,1], the efficiency factor of longitudinal equivalent flexural stiffness drops rapidly from 1.0% to 0.058%, thereafter stabilizing gradually—consistent with predictions from the continuum model and existing research.