Abstract: In view of the poor effect of coal pillar roadway protection in fully mechanized top coal caving mining, large deformation of surrounding rock and gas overflow at the side of goaf, taking the return air roadway of 4209 working face of Jianxin Coal Mine as the engineering background, the reasonable width of coal pillar is 7.8-9.0 m calculated according to the limit equilibrium theory. The FLAC^3D software is used to explore the development law, stress distribution characteristics and deformation of the surrounding rock plastic zone of the roadway under different pillar widths, and the comprehensive analysis show that the optimal width of the coal pillar is 9 m. Based on the simulation results and thin jet sealing principle, combined with the actual conditions on site, the roadway support and thin jet sealing scheme are designed. The practical results show that after the 9 m coal pillar and thin jet sealing technology are adopted, the overall surrounding rock deformation of 4209 working face of return air roadway is small, and the gas concentration is significantly reduced, meeting the safe and efficient production requirements of the working face.