Based on prestress anchoring force value tensioned to anchor cable design one time in working face, the disadvantages of large prestress was analyzed from the aspects of theory, and Xiegou Mine horizontal alleys anchor cable broken was taken as an example, with the explanation of the damage of overlarge of the prestress anchoring force. The results showed that the anchor cable tensioning prestressed construction must be in strict accordance with the split tension, and conduct preservative treatment of anchor cable steel strand, close the roadway and eliminate safety hidden trouble.