maintaining and monitoring power system automation system manually becomes less efficient and impossible in today's power system operations. Based on the situation of shanghai power grid company， the paper discusses the solution for on-line state monitoring， experiences and key issues in building the system. The system uses ACE and XML to solve the problem of crossing over different platforms and unified format storage of data. SOA is applied to supply state monitoring state alarm service. The system highly reduces the burden of engineers and becomes an efficient way of maintaining power system stability and reliability.