In this paper a domain including different major fields is called multiple majors domain. For example, the high-speed railway domain consists of maintenance engineering, traction power supply, EMU and operation management, etc. Ontologies of the major fields are built based on thesaurus and thematic words, and these ontologies are integreted into a unified ontology for the multiple majors domain. Oriented to the domain that consisting of several major fields, this paper gives the ontology model for multiple majors domain, and also builds the model to compute semantic similarity between concepts for multiple major domain. Then, this paper puts out a semantic retrieval system for the knowledge of multiple major domain based on ontology and verifies it. The experimental results show that the developed semantic retrieval system can reach satisfying recall and precision.