The Hebei Haoshi modular office building project exemplifies a multi-storey steel structure modular construction. This study, grounded in the practical implementation of the project, delves into the selection of modular units, the design of joints, and the analysis of the structural system. Firstly, in order to enhance the on-site construction and installation efficiency of modular building units, we propose a novel inter-module clamp-bolted joint. The mechanical properties of this joint are investigated through refined numerical simulations. Results indicate that the joint can be safely simplified to a hinged connection, in accordance with the connection stiffness classification curve of the European Code (EC3). Then, considering the force transmission characteristics of the modular discontinuous floor, we established a comprehensive structural model using MIDAS/GEN. The structure was analyzed and designed under various load combinations. The results demonstrate that performance indices such as periodic vibration mode, interstory displacement, beams and columns stress ratio comply with the requirements of the Code for Seismic Design of Buildings (GB50011-2010, in Chinese). Finally, an elastoplastic time-history analysis of the entire structure under seismic action was conducted, accompanied by supplementary checks for connections at critical positions. The results confirm that these connections meet the design requirements for bearing capacity.