Abstract: In order to design the width of barrier pillar reasonably,the "JC" method for reliability is used.Limit state equations for reliability of barrier pillar are given after analzing randomness of hydraulic pressure,tensile strength of coal bed and coeffcient of water inrush.This paper calculates reliability index,lose efficacy probability and safety coefficient corresponding to the width of different barrier pillar.In contrast with other accidents,the lose efficacy probability of the barrier pillar ranges suitably in 1×10 ^-5~1×10 ^-6.