The utility model relates to a monitoring device capable of avoiding the folding defect during the production of high-speed wires. The monitoring device comprises a rear guide wheel mounted between a front rolling mill and a rear rolling mill, and is characterized in that a front guide wheel is mounted in front of the rear guide wheel; an upper height measuring roller and a lower height measuring roller which correspond to each other are mounted between the front guide wheel and the rear guide wheel, and are respectively connected with a pressure rod of an upper loop pressing device and a pressure rod of a lower loop pressing device; a connecting rod and a stepless sliding resistor are connected between the upper height measuring roller and the lower height measuring roller; the stepless sliding resistor is fixed with the lower height measuring roller; and a contact on the connecting rod slides on the stepless sliding resistor. The utility model has the advantages of simple structure and convenience in use; as the device can monitor in a timely manner whether a workpiece to be rolled normally enters a mill roll for rolling or not and which rolling mill is broken down, timely adjustment is achieved, which has remarkable significance of guidance on the on-line adjustment of the rolling mills; and the device can reduce the rejection rate of rolled pieces due to folding, so as to improve the yield.