Leakage fault is one of the popular problems of cable terminals hindering the safe operation of cables, and there is no clear detection means at present. This paper proposes a detection method of terminal leakage fault based on infrared thermography. Firstly, the numerical simulation model of oil leakage is built, the formation mechanism of surface temperature difference caused by oil leakage in terms of the basic principles of heat transfer is analyzed. Then, the above mechanism is simulated and verified through finite element method. Simulation results show that the temperature difference of terminal surface corresponding to air layer and silicone oil layer increases gradually with the decrease of liquid level. Finally, by comparing the infrared detection with terminal disassembly, the feasibility of applying infrared thermography to the leakage detection of cable terminal is verified.