With the aim to overcome the difficulty of determining rational width of small coal pillar protecting roadways driven along gob area in fully mechanized top-coal caving face(FMTC face),a method to determine the reasonable width of small pillar,combining in-situ measurement,numerical simulation and theoretical calculation,was put forward.The engineering practices indicate that the width of coal pillar determined by this method is reasonable and reliable,and can be used as a scientific basis for the reasonable layout of roadway and the parameters determination of coal pillar protecting roadway in FMTC face.