Abstract: The 27.5 kV cable is an important infrastructure for the traction power supply system of high-speed railway, and its operation is directly related to the safety and operation quality of high-speed railway transportation. Firstly, the working principle of the cladding protector is analyzed, the differences between the three-phase power cable and the single-phase 27.5 kV cable for electrified railway is analyzed, and the current status and existing problems of the current sheath protector for electrified railway 27.5 kV cable are summarized. Secondly, the grounding method of 27.5 kV cable is summarized, and then for the 27.5 kV cable with different conductor sections, different outer sheath insulation materials, and different number of shielded copper wires, the grounding wire, rated voltage, starting operating voltage, continuous operation voltage, nominal discharge current, residual voltage under nominal discharge current, power frequency withstand voltage, withstand high current surge voltage, current capacity, cable sheath minimum impact voltage, residual voltage, action number life and other parameters are studied in detail. And the parameters of the cladding protector are proposed, which has certain reference significance for the standard designation and selection of electrified railway cladding protector.