Abstract: The elastic mechanics theory is used to simplify roof in large working face into beam structure, and the paper analyzes instability types of rock after main roof first breaking and periodic breaking, studies the main factors influencing the stability of the roof structure, points out the conditions of sliding instability caused by structure and the rotary instability, and expounds the instability types of roof strcture at large mining height working face.The results show that the ratio of height and length of rock block after old roof breaking plays a key role in the stability of structure, which ensures the safety production of working face with large mining height.