In order to meet the needs of green environmental protection for energy conservation and emission reduction, and make full use of the advantages of good heat resistance and stability of molten salt, an electric heating furnace with indirect heating of molten salt was developed. Based on the natural convection model and Boussinesq hypothesis, the flow and heat transfer characteristics of molten salt and heat transfer oil in the enclosed space of the indirect heating furnace were studied by numerical simulation method, and the effects of different surface thermal strengths on the flow and heat transfer characteristics of the indirect electric heating furnace were compared. The results show that the density difference and temperature difference caused by the expansion of molten salt in the furnace after heating form a natural convection heat transfer in a confined space, and the average flow velocity of molten salt is 0.00613m/s when the surface thermal strength is 100%. The average temperature is 409.3°C, and a symmetrical annular circulation flow is formed on the cross-section of the electric heating tube from the bottom of the high-temperature heating tube to the upper heat transfer oil pipe, which strengthens the natural convection and heat transfer effect in the furnace, and the overall flow field and temperature distribution in the furnace are stable and uniform, and the heat released by the electric heating tube increases the inlet and outlet temperature of the heat transfer oil by 13.1°C through the indirect heating of molten salt of the intermediate medium, which can meet the process requirements. When the thermal intensity exceeds 100%, the natural convection circulation of molten salt in the furnace is significantly enhanced, the turbulence degree increases, and there is an obvious velocity boundary between the molten salt above the electric heating tube and the surrounding area, which positively affects the flow and heat transfer characteristics in the furnace.