Abstract: Reasonable determination of the size of the coal rock pillar is of great significance to ensure the safe and efficient production of the working face.Taking the actual geology and mining conditions of 132203 working face of Xiaobaodang No.2 Coal Mine as the engineering background, theoretical analysis, engineering analogy, and discrete element numerical simulation were used to analyze the overburden fissure evolution law and the safe coal rock pillar size in the process of mining.The study shows that the number of shear cracks is always larger than the number of tensile cracks in the process of mining, and the damage form of the roof is mainly in the form of shear damage.On the basis of judging the hardness of overburden rock as medium-hard type, the minimum width of the critical waterproof(sand)coal rock pillar for safe mining in the working face is calculated to be 14.99 m, at which time the water-conducting fissure zone will not affect the upper aquifer.The research results can provide a reference for solving the problem of safe coal rock pillars in the working face under similar geological and mining technology conditions.