Disclosed is a DC heating power supply for a transformer. The power supply comprises a three-phase AC power supply, a three-phase bridge rectifier circuit, a filter circuit, a switching circuit, and afollow current circuit, wherein the three-phase AC power supply is connected with the input end of the three-phase bridge rectifier circuit, and the output end of the three-phase bridge rectifier circuit is connected with the input end of the filter circuit; the output end of the filter circuit is connected with the input end of the switch circuit, and the output end of the switch circuit is connected with the input end of the follow current circuit; the output end of the DC heating power supply is connected with the transformer. During heating, heat is generated from the insulating interiorof the transformer, so that the heating efficiency is very high, the consumed time is short, and the dehumidification effect is remarkable. Moreover, when a transformer winding is electrically heated,the heating power can be adjusted by adjusting the voltage of a power supply applied to the primary side to meet the temperature requirement, and the method is suitable for delivery and on-site heating and drying of the transformer.