The knowledge in the closed-loop lifecycle management system is independent and can't be shared. In order to solve the problems, aiming at the characteristics of the closed-loop lifecycle, a new knowledge integration and semantic annotation method was proposed. Firstly, the connotation of knowledge integration and semantic annotation in closed-loop lifecycle management system was expatiated briefly. Secondly, a multi-dimensional and multi-level knowledge integration framework was constructed by using ontology technology for low temperature plasma equipment. Then, on the above basis, a computing method of extracting and matching the document semantic vector and ontology semantic vector was designed. The knowledge document semantic annotation of one sub-system in low temperature plasma equipment was completed. Finally, the test experiments were designed and verified. The experimental results show that, by using knowledge document data set in the closed-loop lifecycle management system to complete the semantic annotation, the average accuracy rate of the proposed method is 84%, and its average recall rate is 79%. The proposed knowledge integration and semantic annotation method can realize the sharing and reuse of the knowledge document in the closed-loop lifecycle management system.