In recent decades, knowledge graph plays an increasingly significant role in intelligent information services. However, for some domains, knowledge graphs are constructed for special purposes and disconnected with each other, which fails to take advantage of knowledge from different knowledge graphs. To this end, we are motivated to propose the concept of knowledge graph federation. In this keynote, we first discuss the issues about knowledge graph federation, and then we introduce two technologies of automatic knowledge graph construction, i.e., relation extraction and entity alignment. The issues in this keynote will provide guidelines for the development of knowledge graph technology.