DC ice-melting is one of the effective measures to prevent low temperature and freezing disasters in a power grid. The operational reliability of a DC de-icing device is very important during the icing period. This paper first introduces the topology of a full bridge modular multilevel DC de-icing device, and reveals the oscillation phenomenon on the DC side of the DC ice-melting device in the de-icing working state. Secondly, the oscillation mechanism of the ice melting device is analyzed and suppression measures are proposed. That is, a nonlinear filter is introduced in the DC voltage feedforward link to suppress high-frequency resonance. Finally, simulation and experimental verification show that the phase-frequency characteristics of the ice melting system impedance have been greatly improved, and the control system can be unlocked and boosted normally. This proves the effectiveness of the suppression measures and reduces the risk of high frequency oscillation. This work is supported by the National Natural Science Foundation of China (No. 52067004).