This paper analyzes the cause of cable-joint burning in railway electrified section considering frequent fire accidents in this section in recent years, followed by the design of a cable-joint online monitoring device for the running state and an overcurrent protection device, with PTC thermistor as the core. PTC overcurrent protection device can cooperate with the sheath-overpressure protector to prevent cables from heating rapidly even burning out by excessive current and from a transient overvoltage breakdown. Meanwhile, the cable-joint online monitoring device can monitor the running state online in real-time based on multi-parameter, thus enabling the staff to accurately evaluate cable-joint condition, make timely warning, adjust the cable load, and rationally develop the cable head maintenance plan. The monitoring device has been applied in the Xiangyu-Line, and it works well. This work is supported by Science and Technology Program of Xi’an (No. 2017080CG/RC043 (XALG026)).