Abstract: According to the effect of F₂₄ large reverse fault on multi seams mining in Pansan mine,the evolution of stress and plastic zone at the different size of preserving fault pillar in 11 coal seam and 13 coal seam were studied by using FLAC^3D,and then the rational size of safe coal pillar was put forward.With the decrease of 11 coal pillar,it was found that stress concentration transfer to the hanging wall of the fault,and the stress concentration zone at left goaf increases gradually because of the influence of 11 coal seam mining to 13 coal seam mining.At the same time,the plastic zone near fault gradually increases and is connected with the stope at last.To prevent water inrush,the pillar of 40 meter and 60 meter are determined respectively.It is proved that the sizes of pillar are rational on field engineering.