Abstract: In order to solve the problem that the high-voltage DC power supply system of the communication base station of the intelligent fire protection system in the open-pit coal mine area has the risk of personal electric shock when the insulation of any branch decreases, an on-line insulation protection of the high-voltage DC power supply system cable based on the signal injection method is proposed. We discuss the principle and method of HVDC power supply cable insulation on-line detection technology, and design a leakage fault detection system for HVDC power supply system. The leakage simulation experiment of HVDC power supply system cable is carried out through eight lines of different lengths and different degrees of insulation drop successively. The research results show that when the leakage of eight power cables of different lengths occurs in the HVDC power supply system, the on-line insulation detection system can accurately select the line of leakage fault and measure the degree of insulation decline, and the error is within the range of ±5%. The leakage protection device provides a guarantee for personal electric shock safety.