Abstract: Selecting reasonable coal pillar size is the premise of success and safety of gob side entry driving. Taking 30503 working face of a coal mine as the background, the reasonable size of narrow coal pillar in gob driving roadway under the condition of overlying residual coal pillar and adjacent goaf of the coal seam is studied by using the methods of theoretical analysis, numerical simulation and field practice. Results have shown that: through theoretical analysis of the stress change law of the remaining coal pillars along the floor, it is determined that the size range of the narrow coal pillars should be between 7 m and 10 m; numerical simulation is used to analyze the stress, deformation and failure law of coal pillar under different widths of coal pillar. Comprehensive theoretical analysis and numerical simulation show that 8 m coal pillar is suitable. Field monitoring results show that when 8 m coal pillars are left, the maximum deformation of the roof of the goaf roadway is 359 mm, the deformation of the two sides is 66 mm, and the surrounding rock deformation of the roadway is stable, which can meet the actual production requirements on site.