Abstract: This paper analyzes current situation of state maintenance and decision support systems used in State Grid. The analysis results show that unified model is the key to architecture of online state maintenance systems. Based on model driven architecture， this paper proposes a Platform Independent Model（PIM） of state maintenance and decision support system. In view of collection， storage， state evaluation and decision， this paper gives a reference architecture of PIM for online state maintenance and decision support system.

Key words: relay protection, state maintenance, state evaluation, MDA, PIM, model