With the development of Prognostics and Health Management (PHM) technologies and the increasing intelligence level and informatization level of the device,the knowledge in PHM domain is increasing.Knowledge graph technology attracts attention from scholars in this domain owing to its powerful knowledge organization,management and representation capabilities and its support for related data/knowledge-driven approaches.Oriented to PHM domain,the concepts,key technologies,applications,challenges and prospects of knowledge graphs are reviewed.Firstly,the definition and components of domain knowledge graphs are introduced.Secondly,the methods of domain knowledge graph construction are discussed,and the common construction modes and technologies in the domain are briefly summarized.Then,in view of the characteristics of knowledge in the domain,the applications of knowledge graphs in the domain are introduced in detail.Finally,the challenges and directions of knowledge graph research for the domain are analyzed.The overview aims to help researchers deepen their understanding of knowledge graph and its application in PHM domain,so as to promote further development and innovation of knowledge graphs applied in this domain.