To clarify the seismic failure mechanism and develop a seismic performance evaluation method for prefabricated metro station structures in liquefiable sites, this study takes Shuangfeng Station of Changchun Metro Line 2 as an engineering case and establishes a three-dimensional soil-structure interaction numerical model using the finite difference software FLAC3D. The evolution characteristics of soil pore water pressure as well as the response laws of displacement and stress of the prefabricated station structure under different ground motions are investigated. Combined with the quasi-static test results of the prefabricated station structure, the seismic damage evolution process and failure mechanism are analyzed, and a dual-parameter seismic performance evaluation method simultaneously considering the global inter-story drift ratio and the opening amount of mortise-and-tenon joints is proposed. Subsequently, seismic fragility analyses are conducted based on both scalar and vector-valued ground motion intensity parameters. The results indicate that when the peak ground acceleration (PGA) is ≥0.2g (g as gravitational acceleration), significant liquefaction occurs in part of the site, and the onset time of liquefaction is markedly advanced with increasing ground motion intensity; the degree of liquefaction near the structure is generally lower than that in the area far from the structure. Liquefaction-induced stiffness degradation and non-uniform ground deformation significantly alter the structural load-transfer path; structural damage is mainly concentrated in the central column and the mortise-and-tenon joints of the sidewalls, exhibiting a progressive evolution from the ends of the central column toward the sidewalls and the connection zones of the arch roof and bottom slab. Even under a low axial load ratio, the central column remains the most vulnerable component. The proposed dual-parameter evaluation criterion enables a more rational assessment of seismic performance. Compared with conventional scalar intensity measures, vector-valued intensity measures more comprehensively reflect the influence of ground motion amplitude and spectral characteristics on structural failure probability, thus obtaining more reasonable fragility assessment results. The findings can provide references for the seismic design and performance assessment of prefabricated metro station structures in liquefiable sites.