The DC de-icing device based on a three-phase rectifier circuit generates a significant amount of harmonics during operation, affecting the safety of other electrical equipment in the power system. The harmonic suppression measures must be taken with the application of DC de-icing devices. In this paper, the ice-melting current parameters of the overhead ground wire in ±800 kV UHVDC transmission line are calculated. The harmonic and the reactive power characteristics of the mobile DC de-icing device using a 6-pulse three-phase fully controlled rectifier are theoretically calculated and simulated. The influences of the rectifier transformer and the rectifier triggering angle on the harmonic and the reactive power are studied, and the single tuned filters of the DC de-icing device are designed in this paper. The simulation results show that installing the Y/Δ-connected rectifier transformer and reducing the triggering angle during the DC de-icing operation can reduce the harmonic content and reactive power of the DC de-icing device. Based on the reactive power demand of the DC de-icing device, the parameters of fifth, seventh and 11th single tuned filters can be designed according to the proportion of each harmonic current, and Δ-connected the filters can be installed on the secondary side of the rectifier transformer. This filter design scheme can simultaneously meet the requirements of the harmonic suppression and the reactive power compensation of the DC de-icing device under different ice-melting currents.