The knowledge graph has been proposed by Google as a knowledge base to enhance its search function, and has been rapidly developed in recent years. As the value of knowledge graphs is constantly being explored, many domain knowledge graphs are rapidly being built. This study clarifies the definition of domain knowledge graphs by comparing domain knowledge graphs with general knowledge graphs, introduces the architecture of domain knowledge graphs, and uses medical knowledge graphs as an example to explain the construction techniques of knowledge graphs. Finally, this study introduces the development of the current popular domain knowledge graphs, and provides a comprehensive summary of the current domain knowledge graph status.