In order to realize the whole process automation of power grid operation, it is necessary to construct a comprehensive general knowledge model in the field of power dispatching operation. In this paper, the intelligent operation knowledge model (IOKM） with good scalability is designed with the machine intelligence of power dispatching operation as the goal, and two knowledge representation modes of hierarchical first-order predicate logic rule base and knowledge ontology are integrated. IOKM is divided into three layers: element knowledge, ontology knowledge and logic knowledge. According to the characteristics of dispatching management, the descriptive attributes and structures of dispatching task ontology, topology ontology and power outage plan ontology are enriched. In order to instantiate the ontology model and apply the rules based on object description to operational examples effectively, this paper proposes a dynamic construction method of fact database. An extensible and concise expression of the priority sequence of operation rules is designed for the synthesis task of operation sequence with time sequence constraints. Taking the actual power outage plan in grid dispatching as an example, the construction and application process of the knowledge model is demonstrated, and the performance of the model is verified.