The invention relates to a cable anti-theft device and a method thereof, belonging to the field of cable anti-theft. In the cable anti-theft alarm device, the cable includes a cable core, a protective layer outside the cable core and a sheath wrapped outside the protective layer. The device includes an alarm unit, a control center, a disconnection detection unit and a distance measuring unit. The control center outputs The signal is sent to the alarm unit and the distance measuring unit, the input end of the disconnection detection unit is connected to the distance measurement unit, and the output end of the disconnection detection unit is connected to the control center. The disconnection detection unit used in this device uses the volt-ampere characteristics of the triode and combines the control center to detect the tiny current in the circuit under test to judge the disconnection of the transmission line. Once a disconnection occurs, it can quickly measure the distance and alarm. In order to reduce economic losses, avoid false alarms of the existing detection circuit and the circuit is very simple, and solve the problem of relatively high false alarm rate of the cable anti-theft alarm device in the prior art.