[Purposes] This study aims to investigate the influence of the single?scale and multi?scale models on the mechanical properties of the structure. [Methods] The large cantilever steel structure of Taiyuan south railway station roof is taken as the research object, the static full?scale test and theoretical analysis are carried out for the key joint (68# tubular joint). A detail construction method of “concrete + transverse diaphragm” was proposed and compared with the original joint construction method. Meanwhile, the single?scale model of the whole structure and the multi?scale model of key joints are established based on the midas Gen software. Then, the mechanical properties such as stability and dynamic response of the structure are particularly discussed. [Findings] Compared with the original joint construction, the bearing capacity of “C40 concrete + 5 transverse diaphragm” detail construction meets the requirements and has certain economy; Compared with the single?scale model, the overall stress of the multi?scale model structure is reduced by 9.70%; In the multi?scale model, the stress of the key joint is significantly different from that of the single joint, and the deformation and stress are reduced by 6.53% and 25.73%, respectively. [Conclusions] The multi?scale model can more realistically simulate the mechanical characteristics of the structure, and the results are more accurate.