Abstract: Fault zones often appear as graben and ladder in the strata, in order to study the width of plastic zone of water proof coal-rock pillar of graben faults, taking the graben faults in Liuzhuang Coal Mine in Huainan Mining Area as the research object, based on the development laws of the height of fractured water-conducting zone, mechanical model of stability of trapezoidal waterproof coal-rock pillar of graben faults is innovatively proposed. According to the stress and its geometric characteristics of local rock mass in trapezoidal coal-rock column, the formula for calculating the failure width of plastic zone of waterproof coal-rock pillar of graben faults is deduced, and F₁₉ and F_19-7 graben faults in Liuzhuang Coal Mine in Huainan Mining Area is studied. Through theoretical analysis and numerical simulation, the width of the plastic zone of waterproof coal-rock pillar of graben faults is calculated to further verify the correctness of the theoretical analysis.