Abstract: Aiming at the problems of large temperature difference inside and outside silicon rods, frequent core melting and rod cracking, and high unit power consumption caused by traditional power-frequency power supply of polysilicon reduction furnaces in the improved Siemens process, a transformation scheme of composite power supply with parallel superposition of power frequency and high frequency is proposed. Firstly, the temperature field distribution mechanism under the skin effect of silicon rods is analyzed, and the development status of high-frequency heating power supply technology at home and abroad as well as the shortcomings of existing schemes are summarized. A phase-separated parallel high-frequency power supply architecture suitable for 40-pair six-phase and 60-pair nine-phase reduction furnaces is designed, and a fully digital IGBT high-frequency power unit including rectifier, chopper, inverter and resonant circuit is constructed, matched with an adaptive frequency-tracking PI coordinated control strategy. The transformation scheme is compatible with the original power-frequency power cabinets, and water-cooled copper tubes are adopted as high-frequency output busbars to realize upgrading without major modifications to the furnace body. Field test results show that the composite power supply mode can limit the temperature uniformity error of silicon rods within ±5 °C. Under the same surface deposition temperature, the total heating current is significantly reduced, the unit power consumption of the reduction process is lowered, shutdown failures caused by thermal stress are mitigated, and the compactness and product quality of silicon rods are improved simultaneously. The innovations of this paper lie in the deep coordinated superposition of power-frequency and high-frequency power supplies, low-modification compatible transformation of existing equipment, and digital adaptive control for wide load impedance, which can provide engineering references for energy-saving electrical transformation of reduction furnaces in the polysilicon industry.