Abstract: Based on the engineering background of old goaf water hazard control in the third coal mine of Yangquan, the lateral boundary prediction of water conducting fracture formed in roof is studied by use of engineering detection and numerical simulation. A method which uses the quantity of horizontal deformation as the criterion for water conducting fracture is proposed. According to the measured values of the lateral boundary of water conducting fracture which comes from the old goaf near the work face K8101, a criterion for water conducting fracture is determined, that is . Based on the criterion, the lateral boundary of water conducting fracture for work face K8404 is predicted, and the water drainage plan for the nearby old goaf is proposed.