Abstract: Confirming the thickness of the isolated mining pillars is the main important problem of openpit to underground mining and mining under quaternary system.Taking the mining engineering under quaternary system for an example,according to the disaffinity airport boundary conditions of isolated pillars and the form of damage mechanism of in the different stress condition,the MohrCoulomb and Tensile failure criteria are used to evaluate.The stress of inside the pillar unit is calculated by the FLAC3D software,and the safety coefficient method based on unit is put forward to calculate the safety coefficient of the isolated pillars.Finally,the reasonable thickness data of the isolated pillars is determined.