Temperature monitoring is important for the operation management of cable joints. However, owing to the problems associated with calculation cost and parameter determination, existing research can only calculate the local temperature with limited accuracy in the operation stage. This does not enable temperature management and condition assessment. Therefore, combined with the analytical, numerical, and inverse analysis methods, a real-time reconstruction method of the 3-D temperature field for cable joints is proposed. In this study, the temperature distribution of the cable joint is analysed by the combination of the Ohm's law and heat transfer rules. The transient heat transfer process is transformed into a stable state heat transfer process under discrete-time conditions using the equivalent analysis method. The inverse problems aimed at identifying the surface heat transfer coefficient and the equivalent current are constructed, which can be solved by iterative calculation. The temperature experiment platform is then built to verify the proposed method. The reconstruction results are consistent with the experimental ones and meet the accuracy requirements of the operation analysis. Finally, the influence of current fluctuation, heat dissipation condition, and measurement accuracy on reconstruction results are analysed. The results show that the proposed method realizes the real-time reconstruction of the temperature field, which is reliable, robust, and anti-interference. It promotes the practical applications of temperature monitoring.