Abstract: In order to determine the rational width of coal pillar of the NO.8215 coalface with fully mechanized top coal caving，the theoretical calculation and numerical simulation analysis were applied to determine the width of coal pillar．The rational width of coal pillar was 6.57 m to 7.67 m through the theoretical calculation，six kinds of width design scheme were proposed，and the UDEC software was adopted to analysize the surrounding rock’s deformation effect．When the coal pillar′s width was 6 m to 7 m，the relative distortion between roof and floor was 480 mm to 500 mm，and the relative deformation of two sides was 380 mm to 420mm，and the value of the vertical stress in the centre of the pillar was 13.08 MPa to 14.11 MPa，and the peak of vertical stress of the floor under the coal pillar was 18.6 MPa to 21.1 MPa．The width of coal pillar was 8 m at the scene，the relative distortion between roof and floor was 220 mm to 460 mm，and the relative deformation of two sides was 340 mm to 620mm，the separation amount were 0.3~7.4mm and 0.3~8.6mm in the roof of the roadway．The project application effect indicated that the width of the coal pillar was reasonable，and the satisfactory technical and economic effects were obtained．

Key words: driving roadway along goaf, narrow coal pillar, surrounding rock control, numerical simulation