Abstract: Two kinds of mechanical model are used to analyze coal wall stability of fully mechanized caving face with great mining height, the research shows that instability position of coal wall is away from the roof of 0.35~0.5 times of the mining height. And simplified the spalling coal body into a single sliding surface model, a stability coefficient K is got through the mechanical analysis. if K ＞1, glide force is bigger than resistance and rib spalling happens; if K =1, coal wall is in limit equilibrium state; if K ＜1, this means that wall is stable. In addition, from the expression of K , it concludes that as the greater of the internal frictional angle and cohesion of coal is, the greater stability of the wall is; when mining height and roof pressure increases, the wall is easier to spall. According to the field practice, taking the steps that injecting Malisan to enhance coal shear strength, strengthening the roof and wall's support, speeding up the work-face advance rate, and removing the frame in time and so on could reduce rib spalling and enhance the stability of the coal wall.