Abstract: Aiming at the serious problem of rib spalling in fully-mechanized caving mining of extra-thick coal seam under a thick and hard roof in northern Shaanxi mining area, the mechanical model of cantilever beam with thick and hard roof and the mechanical model of coal wall rod structure are constructed to clarify the relationship between the critical bearing load of coal wall and the height of coal wall. The co-evolution law of overburden displacement field and working face stress field under the condition of thick and hard roof is studied, and the corresponding relationship between top coal caving and coal wall stability under different mining and caving ratios is revealed. The results show that: ① The critical bearing load of coal wall is inversely proportional to the height of coal wall. The higher the height of coal wall, the lower the critical bearing load and the worse the stability of coal wall.② Under the condition of thick and hard roof, the initial pressure is severe, and the stress concentration in the advance area of the working face increases sharply. The larger mining and caving ratio is not conducive to the maintenance of coal wall stability.③The smaller the mining and caving ratio, the better the stability of the coal wall, the weaker the crushing effect of the top coal driven by the weak stress of the thick and hard roof, and the worse the caving property.④The top coal cavability is inversely proportional to the stability of the coal wall as a whole. Selecting the mining ratio of 1∶0.8 can ensure that the top coal cavability remains unchanged and greatly improve the stability of the coal wall.