Abstract: Aiming at the problem of resource waste caused by too large protective coal pillar in No.30103 working face of Yayaomao Coal Mine, a calculation model of coal pillar width was established by means of field exploration, theoretical analysis, numerical simulation and field monitoring. This paper revealed the distribution law of stress and displacement and the characteristics of plastic zone under the coal pillars with different widths of 6 m, 8 m, 10 m,12 m and 15 m, and determined the reasonable reserved width of the coal pillar. The borehole peeper was used for monitoring and comparative analysis in the field. The research results show that: when the 15 and 12 m protective coal pillars are left in the Yayaomao Coal Mine, the width is large, and there are a large number of undamaged areas in the middle, resulting in a waste of resources; when 6 m and 8 m protective coal pillars are set, the plastic area is completely through, the bearing capacity is poor, and the damage is serious; when the width of protective coal pillars is 10 m, the coal pillar plastic zone is just in the penetration or non-penetration interval, and there is a certain elastic core area inside the coal pillar, which is slightly higher than the theoretically calculated coal pillar width range of 9.55 m. Through on-site drilling monitoring of 15 m and 10 m coal pillars, it is found that whether the 15 m coal pillar or 10 m coal pillar is affected by mining, the development and expansion of cracks in the coal pillar have little effect, there is a certain range of undamaged area in the coal pillar, and the coal pillar has a certain degree of integrity and stability. The research results provide effective data for other mines under similar conditions.