In view of the long-term operation of power cable in high voltage and high current state, the temperature rise caused by various faults will lead to cable overheating or insulation performance degradation. Based on the analysis of cable structure and temperature field, this paper establishes the finite element model of cable temperature field, completes the thermal analysis of cable trench laying and cable intermediate joint, determines its overheating position through thermal analysis, which provides theoretical support for the layout of temperature sensor. The design scheme of online monitoring system for the cable trench temperature is completed, which can collect the temperature data of the cable trench in real time. This study provides reference for the development of intelligent monitoring of power cables in China.