Abstract: Taking the 2201 working face of Haiwan Coal Mine No. 3 as a case, the overburden collapse patterns during mining beneath open-pit slopes were studied using physical simulation, numerical simulation and theoretical analysis. A structural model of "large cantilever beam and high-position oblique step voussior beam" was established. The mechanism of strong mine pressure in the initial mining stage under the open-pit slope was revealed. The results show that due to the existence of the open-pit slope, the continuity of the stratum is cut off, and the overlying strata and the surface loess layer form a large cantilever beam fracture and subsidence during the initial mining stage of the working face, which destroys the original caving law of the overlying strata and forms the strong mine pressure. When the working face advanced to 160 m, the advanced fracture development depth in loess layers reached 90 m. When the working face advanced to 178 m, the "large cantilever beam and high-position oblique step voussior beam" structure formed, with peak support load exceeding 50000 kN/set, forming the strong mine pressure. By establishing a mechanical model of the "large cantilever beam", the force balance equations of the rock blocks and the support resistance formula were derived, and the mechanism of strong mine pressure caused by large cantilever beam structure was revealed. A hydraulic fracturing layer that eliminates the formation conditions of large cantilever beam was proposed. By using the numerical simulation method of hydraulic fracturing and support resistance monitoring, it is found that eliminating the large cantilever beam structure can avoid the occurrence of strong mine pressure, and has been verified by engineering practice.