The load model for draw-out power winding is established according to operation principle of current transformer， the relationships among power output， second turns， load current and magnetization current is theoretically analyzed when current transformer core is not saturated. Furthermore， its correctness is verified by experiments. Then a novel design method for current transformer draw-out power supply based on power control is proposed. The power output of current transformer draw-out power supply is limited in a narrow range by controlling charge current of farad capacitor， so that current transformer draw-out power supply can adapt for larger range of wire current. Finally， the test result demonstrates that power output of current transformer draw-out power supply is near 1 W for wire current from 30 A～1 000 A.