Abstract: The mechanical analysis of the key stratum structure of the hard roof has achieved fruitful research results, but these analyses are the results of treating the roof strata as “rigid bodies”. In order to more accurately analyze the fracture migration law and mechanical action of the key stratum structure of the hard roof, according to the theory of masonry beam and key stratum, the stope overburden structure model of “low equivalent immediate roof & high masonry beam” is improved. The key block structure of masonry beam breaking is improved from “rigid body” to “elastic-plastic body”, the key block structure model of masonry beam breaking considering elastic-plastic deformation is established, and the mechanical action of the key layer structure of the hard roof and the support resistance of the working face are analyzed. Using Design-Expert software, a five-factor and three-level response surface test scheme is designed. Aiming at the main influencing factors such as the elastic limit strain of the key block, the thickness of the key block, the thickness of the overlying soft rock layer, the length of the key block and the equivalent direct roof thickness, the sensitivity analysis of the single factor and the interaction factor on the support resistance of the working face is carried out. The results show that: Compared with the “rigid body” model, the calculation result of the “elastic-plastic body” model is that the horizontal thrust increases and the support resistance of the working face decreases. The analysis process of the “elastic-plastic body” model is more in line with the engineering characteristics of the material, and the calculation results are closer to the actual stress of the key block structure, so it can more accurately reflect the real mechanical behavior of the key block structure. The influence degree of each single factor on the support resistance of the working face from large to small is, in order, the low equivalent direct roof thickness, the thickness of the key block, the length of the key block, the thickness of the overlying soft rock layer and the elastic limit strain of the key block. It can be seen that although the key factors such as the geometric characteristics and load distribution characteristics of the “key block structure model of masonry beam breaking” have a great influence on the support resistance of the working face, when the ratio of the thickness of the key block to the length of the key block is low, the influence of the mechanical properties of the rock mass on the support resistance of the working face will be significantly enhanced. This is the theoretical significance and engineering value of improving the key block structure of masonry beam breaking from “rigid body” to “elastic-plastic body”. When the length of the key block and the low equivalent direct roof thickness, that is, the factors that determine the geometric characteristics and load distribution of the “high masonry beam” and “low equivalent immediate roof” respectively, interact with each other, the influence on the support resistance of the working face is the most significant. In contrast, when only the factors that determine the geometric characteristics of the “high masonry beam” structure and the load distribution interact, the degree of significance is second. The improved model considers the elastic-plastic deformation of the key block of roof breaking and the dynamic change of overlying load, which can provide a more perfect and accurate theoretical basis for the stability analysis of hard roof in the mining process.