Abstract: The modular fabricated steel frame forms a frame-structure column with modular column-column separation, and its vertical bearing capacity and lateral resistance cannot fully play the role of the modular columns working together. Therefore, such modular prefabricated frame structure are unable to be used in the medium-and high-rise buildings, and it is an aspect that needs to be researched and developed. Aiming at the multi-column combination form in the corner column load-bearing modular structure, this paper uses the outer steel plate method to connect the adjacent module columns, named the combination column. The connection structure form of the column-column combination of outer steel plate is proposed and the mechanics property is analyzed. A refined finite element model of the combination column is established, and the unidirectional displacement and cyclic loading simulation are performed on it. The results show that the horizontal lateral stiffness and bearing capacity of the combination column are significantly improved. Furthermore, the proposed combination column with the outer steel plate opening improves its seismic properties. The outer steel combination column has a fuller hysteresis curve and a higher energy dissipation coefficient, and the carrying capacity and energy consumption capacity have been improved. With the good seismic performance, it is a construction method worthy of popularization and application.