In order to study the reasonable width of small pillar gob side entry in the island fully mechanized top coal caving face of 19 m extra thick seam, taking Z109 working face of Donggucheng Coal industry as the research object, the theoretical value of reasonable coal pillar width of gob side entry is calculated as 7.7-9.1 m by using the empirical formula of limit equilibrium theory.FLAC^3D software is used to establish the numerical calculation model of different coal pillar widths.The stress distribution law of surrounding rock of island working face and the failure characteristics of surrounding rock and coal pillar of gob side entry in the driving and mining stages of working face under different coal pillar widths are analyzed, and the reasonable width of coal pillar is determined to be 8 m.Through field measurement, the deformation of surrounding rock during tunneling and mining is obtained.The measured results show that the deformation of surrounding rock is effectively controlled, and the coal pillar width is reasonably selected.The research results have certain theoretical and engineering significance for guiding the reasonable selection of pillar width in gob side entry of small coal pillar in island fully mechanized top coal caving face in extra thick coal seam.