Abstract: In the polysilicon reduction furnace,all the energy is supplied by the heat generation on silicon rods which are heated up by the passage of electric current.The alternating current（AC） produces the alternating magnetic field,and the oscillating magnetic field induces the corresponding eddy current in the conductor,which causes the phenomenon of skin effect.In the present paper,the coupling model of thermal and electromagnetic field for the silicon rods has been developed by coupling Joule heating equation controlled by frequency and heat dissipation（radiation,convection and reaction energy）.Based on the Joule heating process of silicon rods in a 48-rod polysilicon reduction furnace,the effects of AC frequency on temperature and current density profile within rods arranged in different rings have been studied.The interesting results show that the high frequency current source can generate an even temperature profile and an isothermal region inside the rod can be obtained when the relative frequency RF increases to 10.Therefore,utilizing the high frequency current sourc can decrease the temperature gradient within silicon rod effectively,which provides a method for achieving potential maximum deposition radius.Furthermore,the voltage-current curves of low frequency（50 Hz） and high frequency（10 kHz and 50 kHz） can be predicted by the present Joule heating model,at the same time,a hybrid heating mode of low frequency and high frequency is proposed.