Abstract: By monitoring the core temperature of cable joints we can effectively evaluate the status of cable joints,but it is difficult to measure the core temperature directly as the structure of cable joints could be easily damaged. Therefore,the core temperature is often estimated by skin temperature. In order to improve the calculation accuracy of the cable joint core temperature,a simulation model of the cable middle joint is established in the finite element software COMSOL and the electromagnetic thermal coupling calculation is carried out. The effects of ambient temperature and load current on the core and skin temperature of cable joints are studied. The expressions of the core temperature from the skin temperature and ambient temperature of cable joints are obtained by fitting and analyzing the simulation data under various working conditions. Finally,the validity of the expressions is verified. The calculation method can calculate the core temperature of the cable joint faster and more accurately,which is helpful for the practical application of the state evaluation and on-line monitoring of the cable intermediate joint.