Abstract: Based on the law of overlying strata movement in working face and masonry beam balance theory, analyzes the overlying key strata roof block sinking motion characteristics of gob side entry under working face with large mining height and support of small coal pillar,and the mechanical equilibrium structure formed by the mutual extrusion of blocks and damage to surrounding rock of gob side entry.Discussed the failure characteristics of surrounding rock on gob side entry and engineering supporting performance under large mining height.The results show that a stable semi arch mechanical equilibrium structure is formed in the key fault blocks above gob side entry during the mining of adjacent working faces,this structure plays a reliable protecting role in the surrounding rock of roadway below it,during roadway excavation and the mining of the current working face.So,the support for surrounding rock of gob side entry should be carried out around the semi arch mechanical equilibrium structure.Put forward different parts for the surrounding rock of gob side entry should adopt different support mechanism and parameter,and experiments have been carried out in the coal mine to ensure the safe use of the roadway and achieve better economic results in 5312 working face of Jining No.3 coal Mine.