Abstract: The factor weights for horizontal pillar stability were obtained to analyze the stability of horizontal pillar of the Dongtong' V ore by applying AHP analysis method. The results show that the thickness of the horizontal pillar is the most important factor. The minimum safety thickness of the horizontal pillars is 5 m by using the formula of small deformation of thin plate theory. A numerical model is established to make a further analysis. The stress, vertical displacement and plastic zone of horizontal pillar thickness of 5 m to 9 m are analyzed. It is concluded that the horizontal pillar is likely to collapse when its thickness is less than 7 m.