Taking 14100 working face in No.4 coal seam of Majialiang Mine as engineering background, theoretical calculation method was used to get rational width of setting small coal pillar. At the same time, FLAC3D software was adopted to establish numerical simulation model to demonstrate width of different coal pillars. Stress variation law of roadway during mining and advancing period was analyzed and studied, which obtained that appropriate width of coal pillar adapted to engineering practice was 7m.