Abstract: Large mining height fully mechanized mining technology has significant advantages in thick coal seam mining，but too high mining height will affect the stability of the support. Through the me chanical analysis of the support，the influencing factors of the support instability under the condition of large mining height are discussed，and the limit inclination angle of the support in the free state and different mining height states is obtained. When the mining height is less than 4.2 m，the limit angle decreases with the increase of roof pressure，but the decrease is smaller and smaller. When the mining height is greater than 4.2 m，the limit angle increases with the increase of roof pressure，and the greater the increase. The stability of the support is related to its width. The wider the support is，the higher the stability is. The development trend of support selection in large mining height coal working face is to increase the support width.

Key words: large mining height fully mechanized support, mechanical analysis, limit angle, width of support