With the development of extra-high voltage (EHV), ice melting of EHV transmission line is becoming a research hotspot. The ice-melting device requires large current and capacity for EHV transmission line because of big line diameter and long lines, so the current ice melting is a research difficulty. According to the characteristics of EHV transmission line, the piecewise DC de-icing method is proposed for EHV transmission line which is divided into several segments. The way can effectively reduce the capacity of the ice-melting device by setting DC ice melting point and short circuit point to the line segment of the repeat ice thawing freezing. The de-icing of EHV transmission line needs big DC ice-melting device capacity. In order to reduce the current harmonic distortion rate of melting ice device’s net side, the way using 24 pulse rectifier transformer plus rectifiers is used which can effectively reduce the interference on the grid side power caused by DC de-icing device and decrease the output DC voltage ripple factor. Finally the simulation research on the design of DC ice-melting device for EHV transmission line is taken. The 5th and 7th input harmonic current caused by rectifier can effectively be eliminated using 24 pulse rectifier transformer plus multiple rectifiers parallel mode. The low current total harmonic distortion rate of rectifier transformer’s input current is only 0. 51%. The pulse number is 24 and the voltage ripple factor is only 0. 616 for the output DC voltage. The simulation results prove the feasibility and the correctness of the DC ice-melting device’s design for EHV.