When the temperature of the cable core is too high, it will accelerate the aging of the insulation material, affect the safe operation of the cable, and shorten the service life of the cable. Therefore, a simple and effective way to monitor the cable core temperature in real time is an important measure to improve operation and maintenance efficiency and reduce the risk of failure. There are many problems with the traditional cable temperature measurement methods, such as the large influence of ambient temperature, low measurement accuracy, and high application cost. In order to solve these problems, this paper designs a set of low-power non-invasive high-voltage cable core temperature monitoring system based on the non-invasive high-voltage cable core temperature measurement principle of temperature field construction and sensor array. In this paper, through theoretical analysis and with the help of experiments, we obtain the temperature gradient law of 10kV true high-voltage cable after local wrapping of heat-resistant medium and derive the analytical calculation formula of the cable core temperature.