Ice-coating of overhead transmission lines is harmful to the reliability of ultra high voltage direct current（UHVDC）. This paper discusses two kinds of de-icing schemes for UHVDC. One is preventive and the other is of emergency. In the preventive scheme， the power flows in opposite directions in the two poles， which forms high current and low net power to prevent the formation of ice. In the emergency scheme， dual converters are connected in parallel instead of series-connection mode at each station; high direct currents are formed to melt the ice quickly. The control strategy of emergency de-icing scheme for UHVDC system is presented， the parallel converters at the rectifier side are both in current control， and at the inverter side， one is in current control and the other is in voltage control. The reference value for the current controlled inverter is half of the measured DC line current to balance the paralleled converters， the voltage controlled inverter controls the voltage of whole pole. The proposed de-icing scheme can greatly improve the reliability of UHVDC by mitigating the influence of ice-coating.