Fixed DC de-icer converts AC power into an adjustable DC voltage through thyristor rectifier valves. This voltage is then delivered via smoothing reactors and de-icing transfer disconnectors to targeted transmission lines, thereby forming a DC circuit in the line. The inherent resistance of transmission lines causes a temperature rise when DC current flows, thereby effectively melting ice accretion to achieve the purpose of de-icing. Meanwhile, by controlling the firing angle of thyristor valves, the magnitude of DC current applied to the transmission line can be adjusted in real time and continuously. This allows for precise temperature regulation of transmission lines, enabling safe and effective ice removal. The device can provide safe, efficient, and rapid fully-automated intelligent de-icing for 66kV, 110kV, and above transmission conductors and ground wires in substations vulnerable to ice-snow disasters.