Abstract: In order to study the breaking angle of overlying key strata in stope,based on elastic mechanics and rock mechanics,the beam mechanical model of breaking of overlying key stratum is established,and the calculation formula of rock breaking angle is derived. Simula-tion experiment was carried out to verify the rationality and reliability of the formula through physical simulation. The study shows that ① Theoretical calculation shows that the breaking angle of overlying key strata varies from 57. 5° to 71． 0°,the simulated breaking angle is 50°-70°,the theoretical results are in good agreement with the experimental results which shows that the calculation formula of rock breaking angle has high reliability and rationality;② The breaking angle formula shows that the key stratum breaking angle is related to the physical and mechanical parameters of key stratum,such as,internal friction angle,tensile strength,rock mass density, elastic modulus,rock thickness,and the physical and mechanical parameters of load strata,such as,thickness,rock mass density,and elastic modulus. For the overlying strata of a working face,the change of breaking angle is mainly affected by the thickness of the key stratum itself and the thickness of its load layers;③ When the ratio of key stratum thickness to load strata thickness h / h′1. 5,the increase of the load strata thickness will cause the breaking angle to decrease, the increase of rock thickness leads to the decrease of fracture angle. The effect of the two influencing factors on the breaking angle is the same,and the influence of the change of key stratum thickness on the breaking angle is greater than the change of the thickness of the load layer;⑤ When h / h′ = 4,the change of key stratum thickness and load strata thickness have the same influence on breaking angle.