Modular steel construction (MSC) is a novel structural system comprising of stacked modular units. It represents a type of green building with broad market prospects, which is aligned with industrialization and intellectualization trends. The shear behavior of the inter-module connection significantly impacts the lateral force resistance behavior of the MSC, which directly determines the load bearing capacity of the MSC. However, there are few studies on the shear behavior of the inter-module connection. A fully prefabricated liftable connection (FPLC) for MSC was proposed. The damage mechanism and design method of the FPLC under shear force were systematically investigated. Monotonic shear tests were conducted on six full-scale FPLC specimens. The failure mode, strain distribution, and load-bearing capacity of the FPLC under shear force were discussed. Subsequently, a refined finite element model (FEM) of the FPLC was established using the universal finite element analysis (FEA) software ABAQUS. The accuracy of the developed FEM was validated by comparing the experimental and numerical results. In addition, the development of the internal forces of the long stay bolts of the specimens was discussed to reveal the load-transfer mechanism of the FPLC. Finally, a series of prediction equations for the ultimate load-bearing capacity of the FPLC under a shear force were derived. The reliability of the proposed formulas was validated by comparing the theoretical and experimental results. The present research work will provide a comprehensive understanding of the shear behavior of the FPLC and corresponding design method, which is beneficial for the promotion of the MSC; limitations and future work are also briefly presented.