In view of the adverse effect of the failure mode of the “strong beam and weak column” at the top-layer joint of subway stations on structural seismic performance under high axial compression ratio, a novel assembled steel–concrete composite (ASCC) beam–column joint for the top-layer is proposed in this paper, and its seismic performance is studied through cyclic loading tests and finite element analysis. The findings indicate that, in comparison to the reinforced concrete joint, the yield bearing capacity, ultimate bearing capacity, and ductility of the ASCC joint exhibit increases of approximately 46%, 13% and 40%, respectively, demonstrating superior seismic performance and a “strong column and weak beam” failure mode of the ASCC joint. The impact of parameters including the steel tube thickness, length of the lower steel tube, high axial compression ratio, and bolt quantity on the seismic performance of ASCC joints was further examined using a validated finite element model. Parametric investigations reveal that the ASCC joints with greater steel tube thickness, longer length of lower steel tube, and more bolts demonstrate significant improvements in load-bearing capacity, lateral displacement resistance, and energy dissipation capacity. A value of 0.80 can be recommended as the new high axial compression ratio upper limit of the current code. It is suggested that under the proposed new high axial compression ratio upper limit, the steel tube thickness should be 1–2% of the column diameter, while the length of the lower steel tube should be 1/3 of the length of the lower column, with more bolts restricting the deformation of the extended plates as the design and construction of joints better suit practical engineering applications.