Under the background of energy technology innovation and continuous promotion of marine power development, the actual demand for cross sea power transmission is rising, and the role of submarine cable as a key transmission medium is becoming increasingly prominent. Taking 35 kV three core AC submarine cable as the analysis object, this study built a two-dimensional numerical model with the help of finite element simulation software to carry out in-depth discussion. By establishing an electric thermal physical field coupling model for communication submarine cables, the law of the temperature field of submarine cables changing with external environmental parameters such as conductor current and voltage was simulated and analyzed. Finally, by calculating the steady-state response of overvoltage in the coupling model, the changes in electric field and temperature field under overvoltage were studied. When the submarine cable is single-phase grounded in a neutral grounding system through a small resistor, the temperature of the fault phase increases by 1.69 times, the temperature of the non fault phase increases by 0.74 times, and the maximum value of the electric field increases by 0.59 times. Analyzing the typical fault characteristics and mechanisms is of great significance for the manufacturing, selection, application, operation, and maintenance of submarine cables.