A new design of power supply is proposed to solve the problems existing in current power supply for high voltage transmission and distribution lines online monitoring equipment. Adopt two cores of different materials in parallel,choose appropriate core to work according to the scope of current and combine the induction power supply with the lithium battery power supply. By comparing properties of different core materials, nanocrystalline alloy and silicon steel are selected. The power supply circuit is designed. Experimental results show that the power supply can provide sable power between zero to one thousand amperes and have no power deadband.