Nature, diversity, and openness are what we demand from urban green space in the 21st century. Based on the summary of urban green space connotation, types and significance, this paper reviewed the research hotspots of urban green space, i.e., conservation and planning of urban-rural fringe, restoration and preservation of natural areas and indigenous vegetation, ecological restoration and planning of green way, biodiversity conservation, ecosystem structure and services, and management policy. The difference between foreign and domestic urban green space researches and practices were summarized, and some preferential urban green space research aspects in the future were proposed. It was suggested that in China, urban green space strategy should be integrated into urban planning and land use planning.