A new large-capacity DC deicer/static var compensator（SVC） is developed. Compared with small-capacity DC deicer， it has many characteristics. Because of large capacity and static var compensation， the device contains two 3-winding converter transformers. High-voltage side of the transformers is powered directly from the high voltage grid， mid-voltage side is connected with AC filter banks， and the low-voltage side is connected with thyristor valves. Because of large size of equipment parts， automatic switching function is achieved between deicing and SVC operation mode by changing the position of 14 3-phase electric switches and switching control and protection functions， to avoid human intervention. Because the devices are connected with high operational importance， and the long operating time， the control and protection system is designed to use dual-redundant configuration so as to improve the overall reliability. Field application indicates that when large-capacity DC deicer/SVC operates in deicing mode， it can solve the ice-clad problems of the large diameter， long-distance extra-high voltage（EHV） line effectively. When it operates in SVC mode， it can improve the supporting ability of grid voltage effectively.