Abstract: Based on the theoretical analysis,numerical simulation and laboratory test,the instability mechanism and characteristics of the coal wall under the action of dynamic load are studied. A PFC 2D biaxial compression numerical test model is established,and the fracture is planted in the model to study the scale effect of coal body and coal sample under static load. It is concluded that the number,continuity and distribution of natural defects in coal seam have obvious influence on size effect. The larger the sample is,the lower the strength is,and the change trend is logarithmic curve. Further,the mechanical properties of coal samples under static and dynamic loads are studied by Hopkinson test. It is considered that there is a good consistency between the peak strength obtained from dynamic load test and the stability of coal wall,which reflects the influence of fine joint structure and defects on coal wall stability under the influence of mining. Taking Yangquan mining area as an example,the dynamic and static peak strength of coal samples No. 15 from mine No. 1,mine No. 2,mine No. 5 and Xinjing mine are
compared with the actual height of coal wall stability. It is concluded that the dynamic peak strength of coal sample can better reflect the influence degree of mining stress. on the stability of coal wall,which provides a theoretical basis for the definition of scientific mining height under strong disturbance.