Abstract: In view of problem of misoperation of protection device caused by DC system grounding fault which often appears in substations, the concept of capacitive reactive power of DC system was proposed, and an optimized scheme of centralized power supply of DC system was designed applying optimization method of capacitive reactive power. The optimization scheme reduces DC line-to-ground capacitive character, and achieves the purpose of reducing reactive power by optimizing circuit trail on the basis of meeting supply reliability. It solves the misoperation problem of protection device and improves operating efficiency of DC system. Finally, the effect of the reactive power optimization scheme was evaluated to verify its reliability, security and economical efficiency.