In the process of EH-SAGD (electrical heating-assisted steam-assisted gravity drainage) of heavy oil, there is a lack of understanding of the interaction mechanism between downhole high-power heating cable and SAGD and the heat transfer law of heating cable. Based on the theory of heat transfer and fluid mechanics, a heat-flow coupling calculation model of 400 m wellbore steam circulation electric heating was constructed. The influence of the arrangement of the core wire, the amount of steam injection, the heating power and the steam injection temperature on the temperature field was systematically studied, and the heat transfer mechanism under the synergistic effect of multiple parameters was revealed. The results show that the steam injection rate should not be less than 20 t/d to avoid crude oil coking and cable overheating; increasing the heating power can significantly increase the temperature of steam and core wire. The heating power should be controlled within 2 kW/m to prevent heater failure. When the core wire spacing is greater than 15 mm, increasing the core wire spacing can effectively reduce the local heat accumulation of the core wire. Appropriately reducing the injection temperature can optimize the energy consumption while ensuring the heating efficiency. The research work in this paper provides a theoretical basis for the layout design of heating cables, the optimization of steam injection parameters and the safe operation of heavy oil electrical heating-assisted SAGD technology in engineering practice.