Based on the surrounding rock deformed serious and poor stability of fully-mechanized caving faces gob-side entry problem, through the analysis of gob-side entry instability of mechanics mechanism, the FLAC numerical simulation software was used to simulate the subsidence and horizontal displacement of the coal pillar width and the supporting conditions, the coal pillar width and subsidence and horizontal displacement of the coal pillar along roadway floor in the geological conditions of 5303 fully-mechanized caving was concluded and the most reasonable coal pillar width was settled ultimately.