Substation DC system is the power supplier of protect and communication devices in substation, which plays a significant role for the secure and reliable performance of substation. Onsite substation DC system maintenance required a large number of man power and money in the past. However, with the technique of DC system intelligent maintenance, it will monitor and maintain the DC system automatically. It can discharge and charge battery string online securely via inference-free automatic switch between battery charger and battery system. It can check battery capacity, battery condition and carry out activation for battery string. Meanwhile it can check relevant parameters of battery charger. The intelligent and automatic maintenance system will have wide application and huge marketing potential.