Abstract: For simplifying the mechanical models and the loading patterns in structural mechanics and the design of engineering structures, three methods, including a semi-static loading method, a three-step loading method for simulating the construction process and a multi-layer method, are adopted to study the simplification and the calculation of the mechanical models of frame structures under the action of vertical load. The assumptions made in the calculation by the three methods and the calculation results are analyzed, and reasonable scopes for the application are suggested. The results demonstrate that the semi-static load method is more suitable for the analysis of the progressive collapse and the design and the calculation of the building structure modification while the three-step loading method is more applicable for the design and the calculation of new projects. In addition, as a simplified calculation method by hand, the multi-layer method can be used as a basic method for understanding the principles of structural mechanics.