Abstract: Analyzed the reasons of high undersize rate of lump coal in Jining No.3 colliery coal preparation plant,and on the basis of studying and comparing various technologies of preventing breakage of lump coal,developed screw conveyor system preventing breakage of lump coal that suitable for use in coal bin condition of the plant.The production result shows that the system is better in utilization,make the undersize fraction rate of lump coal decreased form 36.84% to 19.26%,effectively solved the problem of the undersize fraction rate of lump coal exceed standard in this coal preparation plant.