As faults occur in a large-scale power system， all relevant information is submerged in a large event and alarm stream， which makes it very difficult to deal with fault diagnosis through the capability of a single intelligent system based on individual application systems and single diagnostic means alone. This paper proposes a hierarchical fault diagnosis model of a large-scale power system adopting multi-agent system technology and based on dispatch integrated information platform（DIIP）. The results of case studies suggest that the proposed approach is effective and practicable.