Abstract: Aiming at the problems such as large-area rib spalling and inconsistent rules of full-mechanized caving face in “three-soft” thick coal seam, taking Shajihai Coal Mine as an engineering background, the failure forms of working face rib spalling were analyzed and the mechanical model of coal wall system was constructed by using theoretical analysis, numerical simulation and field monitoring, and the mechanism of coal wall rib spalling in “three-soft” thick coal seam was revealed. The effect laws of different cutting height, advancing speed and support strength conditions on working surface were analyzed. The results show that shear failure is the main type of working face coal wall in “three-soft” and thick coal seam in Shajihai Mine, and when the main roof is periodically broken, the dynamic load, direct roof and top coal load are jointly borne by the coal wall and supports, and the risk of coal wall instability increases when the roof is compressed; when the cutting height is in the range of 2.8-3.6 m, the support strength is above 1.0 MPa, and the advancing speed during normal mining and pressure in the general area is greater than or equal to 6.4 m/d and 8.0 m/d respectively, the incidence of rib spalling in the working face is greatly reduced. Based on the effect of key mining parameters on the working face rib spalling, the study puts forward the graded control strategy of the working face rib spalling of full-mechanized caving in “three-soft” thick coal seam, and determines the cutting height, advancing speed and initial support force of the working face according to the mining conditions of the working face and surrounding rock. In view of the difficult area of rib spalling control, the flexible strengthening technology for coal wall in working face with “rubber nylon pipe + grouting” full-length anchoring as the technical core is further proposed, the design method of key parameters such as drilling depth, drilling position and drilling spacing is defined, and related supporting devices are developed, which can control large deformation of coal wall and prevent the further falling of large coal body. The application in B1003W03 working face shows that the control countermeasure technology can effectively alleviate the working face rib spalling, and the application effect is good.