Abstract: According to the engineering geological conditions of 4404 isolated island fully-mechanized caving face in shaoyaohua Coal Mine, the paper studies the reasonable chain pillar size of isolated island full-mechanized caving face by theoretical analysis method and FLAC^3D numerical simulation and field measurement, and analyzes the elastic and plastic zone development situations and the vertical stress distribution laws under the conditions of different chain pillars widths, the results show that there is large enough elastic zone in chain pillar which can guarantee the stability of chain pillars itself and stoping roadway when the chain pillar width is between 20 to 25 m; the vertical stress in coal pillar begin to decrease and presents a double stress state when the coal pillar width is more than 19 m. Combined with observation, the reasonable chain pillar width of 4404 coal face is 20 m.