As an important equipment of the sodium-cooled fast reactor nuclear island plant, the steam generator is responsible for transferring the heat generated by the nuclear reactor to the three-loop water/steam, and a large number of experimental and numerical studies have been carried out in the literature to investigate its thermal characteristics. During the startup of the steam generator from a cold state, it is necessary to preheat the equipment by means of an electric heater arranged outside the steam generator. Steam generators are large and complex, so experiments on prototype structures require extremely high thermal power and high research costs. In this paper, the CFD software Fluent is used to investigate the heating effect of different arrangement forms of electric heaters outside the steam generator, and an experimental study on the heating of electric heaters with equal scale model is carried out for the localization of the steam generator. The results show that the size of the gap between the electric heater and the surface of the steam generator equipment is the most critical factor affecting the heating efficiency. In order to reduce the gap between the electric heater and the steam generator, this paper adopts the addition of stainless steel shims between the two to improve the heat transfer effect. Numerical simulation results and experimental results show that the addition of stainless steel shims can significantly improve the heating efficiency of the electric heater, while reducing the maximum temperature of the electric heater, which is conducive to extending the service life of the electric heater and improve the nuclear power plant economy. At the same time, this study has a good reference significance for the optimization of electric heater arrangement for similar high temperature equipment.