Abstract: Due to the complex geological conditions of 11 mining area of full mechanized caving mining face in Wangwa coal, a reasonable section parameter of coal pillar can play an important role to guide the safety production. The measurement results of the stress and optical peephole device in the coal pillar indicates that 10 m ahead of the working face is the peak stress along the direction of coal pillar, the destroyed region of coal pillar is within 3 m along the direction of inclination, and the stress reaches the peak value around 6 m in the coal pillar. Further, the stress distribution rules of different size coal pillars are obtained by numerical simulation under the production condition here, revealing that the coal pillar gets some elastic region when the width of coal pillar increases to 26 m, with the increase of the width of coal pillar, the width of elastic region also increases, and that when the width of coal pillar increases to 29 m and 32 m, it has been able to guarantee the stability of coal pillar and the deformation of roadway is within the scope of the license. Based on the combination of field monitoring and numerical simulation，the reasonable size of the section coal pillar should be 30 m and the width of coal pillar is greatly reduced comparing with the previous pillar, which greatly improved the recovery rate of coal resources.