Geographic range size of endemic species is the most important indicator of species’ vulnerability to extinction and conservation prioritization, yet variation in range size among species and across space has been relatively understudied. We investigated the variations and geographic patterns of the range sizes of 9,898 angiosperm species endemic to China and compared them with effects of historical and contemporary climate, physiological tolerances of species and species functional traits associated with dispersal ability (including growth form, fruit type and sexual system) on range size variations. Our results revealed that narrow-ranged species are clustered in Southwest China where angiosperm species richness peaks. Winter temperature had the strongest and most negative effects on the range size variations of narrow-ranged species across space and species, while climate seasonality had the strongest and most positive effects on the range size variations of wide-ranged species across space and species. Climate also influenced species range size indirectly via its effects on species' functional traits associated with dispersal ability. Range size of all species, narrow-ranged, and wide-ranged species showed little phylogenetic signal, suggesting that phylogenetic conservatism plays a very weak role in range size variations. Our results show that the range size of angiosperm species endemic to China is driven by both extrinsic spatio-temporal environmental factors and intrinsic species' traits that allow species to cope with environment change.