Abstract: Geospatial data has two important roles, that is, serving as the geospatial reference and using as a source of geographic knowledge. In the past years, its former role has been extensively investigated which leads to in-depth development and wide application of a number of geospatial data and information service. However, mining or extracting knowledge from geospatial data has not been well explored and few geospatial knowledge services are provided to the users. "Massive information, explosive information and rare knowledge" becomes one of the major challenges facing the geospatial societies, and more efforts should be devoted to moving from traditional geospatial data/information service to knowledge service. Firstly, this paper has reviewed the latest development of Knowledge Graph and discussed differences among geospatial data, information and knowledge. Secondly, a conceptual framework is proposed for geospatial knowledge service, which is characterized by structuring building and data linking. Four special requirements for building the geospatial knowledge service are identified. A research agenda is then proposed, including building domain knowledge graph, technological innovation, and developing operational service systems. Finally, the preliminary results of GlobeLand30 knowledge service system is briefly introduced.