Abstract: According to mining conditions of the No.5 coal seam in Cuijiazhai mine,based on the limit equilibrium theory in the three dimensional stress states,this paper deduced the calculation formulas of the limit equilibrium zone width under the influence of mining on both sides of the coal pillar.The theoretical values of coal pillars' width were obtained.Then,stress states of different widths of coal pillar and stress field characteristics in its tilt direction were analyzed by using the FLAC^3D numerical simulation software.In comprehensive comparison with the results of numerical simulation and theoretical calculation,the rational coal pillar width was set as 6~7 m in No.5 coal seam of Cuijiazhai coal mine.In addition,this paper provides the reference for retaining reasonable sectional coal pillars and controlling stability of surrounding rock under complex stress conditions.