Through the analysis of development goals on operation and maintenance of substation secondary equipment, this paper elaborates intelligent operation and maintenance principles of secondary equipment. In order to achieve visual operations, intelligent, customized maintenance operation and maintenance goals, the intelligent maintenance system structure and functions scheme are presented. In terms of technical solutions, it focuses on some key technologies including the visualization technology, intelligent alarms, fault diagnosis and status evaluation technology and so on. All these technologies are effective solutions to solve the current problems on operation and maintenance stages. The intelligent operation and maintenance systems have been successfully used in a variety of demonstration projects and achieved good operating results.