Abstract: In order to determine the size of the section coal pillar under the influence of the working face mining pressure and to increase the coal production efficiency,this paper takes the No.403,405 lane of No.3 Coal mine in the Fucun Coal Mine as a case.On the basis of theoretical calculation and numerical simulation,a three-dimensional discrete element model which takes the influence of the middle stress into account is built.After optimization of the supporting parameters,the distribution of surrounding rock deformation and supporting pressure of the roadway with the coal pillar widths of 3,5,7,9,and 11 m are discussed.The research results show that the theoretical measurement of the coal pillar retention should be 3.25 to 3.85 m.The numerical analysis shows that the deformation of the coal seam along the empty side decreases first and then decreases with the increase of the width of the coal pillar,and reaches a minimum when the coal pillar width is 5 m.The bearing pressure in the coal pillars has a single peak distribution and the peak size increases with the increase of the coal pillar width.When the coal pillar width is less than 5 m,the peak stress is smaller than the original rock stress.The surrounding rock control of dynamic pressure roadway can be left within the stress reduction zone of 0 to 6 m,and the optimal size of section protection coal pillar is 3.0 to 5.0 m.In a field practice,the 3 m coal pillar is placed under the high pre-stressing pressure anchor support system,which has a good surrounding rock control effect,and it provides a reference for the selection of reasonable coal pillar width under similar conditions.