Abstract: In order to determine the width of the isolated pillar under the lateral pressure of the caving rock，FLAC3D was used to simulate the stability of five different widths of isolated pillars.Under the action of lateral pressure，there is obvious stress concentration at the bottom of the isolated pillar，and the tensile stress and horizontal displacement on the side of the goaf are significantly greater than those of the twostep pillar.The stress and horizontal displacement of the isolated pillar decrease with the increase of the width，and the critical width to ensure the stability of the isolated pillar is 15 m.Considering the influence of geological factors and blasting vibration，it is recommended that the width of isolated pillar should be 20 m.

Key words: isolated pillar, caving rock, lateral pressure, open stope method