Abstract: The stability of the surrounding rock of the fully mechanized mining face open cut is a key factor affecting the normal equipment installation and mining of the fully mechanized mining face. Taking the large cross-section open cut of the 112203 fully mechanized mining face in Xiaobaodang No.1 Coal Mine as the research object, theoretical calculation is used to analyze the deformation mechanism of the roof of the 112203 fully mechanized mining face open cut and the theoretical support parameters. The discrete element numerical simulation software is used to establish the UDEC Trigon model, and the influence of support strength on the evolution law of roof crack, failure mode and damage degree in the secondary roadway is studied. The numerical simulation results show that reasonable support technology can control the expansion of roof micro-cracks and reduce the development height of macro-fractures. The rock bridges existing in the roof strata after the combined support of long and short anchor cables can effectively limit the formation of macro-fractures and their interaction, especially the key support in the intersection area can reduce the development height of roof fractures in the secondary roadway and weaken the damage degree of roof strata in the large cross-section open cut. Field tests show that after reinforcement support with extended anchor cables and single hydraulic props, the approaching distance between the two sides of the large cross-section open cut in 112203 fully mechanized mining face is stable at about 350 mm, and the approaching distance between the roof and floor is stable at about 550 mm; there is no obvious delamination on the roof, and the maximum delamination amount on the top plate is 2.4 mm. The method of theoretical analysis and numerical simulation in this paper is helpful to understand the failure mode of the roof of the large cross-section open cut of the fully mechanized mining face and provides a new approach for the design of its control technical parameters.