Abstract: Based on Chang Lebao coal mining reasonable mining size under reamer-pillar coal mining, this paper studies pillar stability by theoretical analysis、numerical simulation and physical simulation. The results show: The existing “mining 10 leave 8” coal mining of Chang Lebao can not guarantee the permanent stability of pillar, The leaving pillar all enters plastic failure under numerical simulation, all leaving pillars occur group instability under physical simulation. When the mining width is 10 meter under reamer-pillar coal mining of Chang Lebao, the leaving width at least is 10 meter. The pillar elastic nuclear area rate is 50.0% under the “mining 10 leave 10” mining method in numerical simulation. This result exceed the 31% of field statistics pillar permanent stability about pillar elastic nuclear area rate in Yu Yang area. The stress distribution of coal-pillar presents gently saddle type. The design scheme can guarantee the permanent stability of pillar and provide reference for the wester mines to protect water resources.