A knowledge management method for AP1000 nuclear is proposed. Based on the modularization characteristic of AP1000, the set of AP1000 ontology is created. Because the first nuclear power based on AP1000 is still being developed, the ontology model of AP1000 is hard to construct now. The particle swarm optimization is adopted to extract the relatively independent instance models from the complexity AP1000 instance model, which map into the conception models called basis ontology. In order to implement the comparison between two conceptions, using the idea of the DNA inheritance in a family, a similarity measure model of the conception is developed. By means of the general-special relation between the conceptions, the similarity measure model and the basis ontology, the knowledge retrieval for AP1000 is implemented.