The surface temperature of cables is an important criteria for determining the operating status and locating faults. To address the issues such as high cost and difficult implementation of manual and wired detection methods, a self-powered wireless temperature measurement system based on magnetic field energy harvesting technology is designed, which consists of two components: the energy harvesting and management module, and the temperature sensing and transmission module. The former module collects and distributes the magnetic field energy around the cable, thereby powering the entire system. The latter module, under the control of a microcontroller, monitors the surface temperature in real-time and transmits the data to the base station via LoRa communication. The experimental results indicate that the designed device is capable of self-powering and provides stable and accurate data transmission capabilities.