A good knowledge of species diversity is essential for urban forest planning and management. In this study, we analyzed species diversity of urban forests in China using data synthesized through a systematic review. Our analysis showed that 3740 taxa of woody plants at species level and below have been reported in urban forests in 257 cities. Merging to the species level, there were 2640 species, including 1671 trees, 743 shrubs, and 226 lianas. Salix babylonica L. was the most widely distributed urban tree species in China. Overall, native species accounted for 76.02% of the observed species while the rest were exotic species. Inside cities, parks contained more species than other types of land use. Among cities, composition similarity of urban forests decreased as spatial distances among them increased. Besides, there was a latitudinal pattern in compositional similarity of urban forests in China. The relatively low ratio of the number of woody plant species in urban forests to these naturally distributed in China indicates that there is plenty of room for increasing species diversity of urban forests in China. However, cautions must be taken to avoid increasing compositional similarity of urban forests in China at the same time.