Many community characteristics depend upon the distribution of species among functional entities (unique combinations of functional traits). Understanding these distributions is fundamental to conserve biodiversity and maintain ecosystem functions. We distinguish between common species (more than one individual per hectare) and rare species (less than one individual per hectare) based on species richness in the southern subtropical evergreen broad-leaved forest community of Dinghushan, Guangdong Province. In this study, based on functional entities, the number of functional entities, functional redundancy, functional vulnerability, and functional over-redundancy were calculated separately to describe the functional diversity of common and rare species. Wilcoxon test method was used to detect the differences in functional traits among common and rare species. Linear regression was used to analyze the relationship between the functional diversity of common and rare species and the number of species. RDA(Redundancy Analysis) was used to analyze the environmental factors affecting the functional diversity of common and rare species. The results showed that:(1) There were significant differences in functional traits among common and rare species of the subtropical evergreen broad-leaved forest in Dinghushan. (2) The lower number of rare species in the community maintained a higher proportion of the number of functional entities. The number of functional entities was significantly and positively correlated with the number of common and rare species, and the number of functional entities increased much more rapidly with the number of rare species than with the number of common species, suggesting that communities with high abundance are less sensitive to species loss. The functional redundancy was significantly and positively correlated with the number of species of common and rare species, suggesting that southern subtropical forests with high species numbers are more resistant to disturbance. The functional over-redundancy was significantly and positively correlated with the number of rare species, indicating that rare species have a higher density of species in their functional entities. The functional vulnerability was significantly negatively correlated with the number of species of common and rare species, indicating that species-rich communities moderately reduced potentially functional vulnerability, but the degree of vulnerability remained higher in species-rich communities. (3) Elevation was a significant topographic factor affecting functional diversity of common species, and relief was a significant topographic factor affecting functional diversity of rare species. Soil water content was a significant soil factor affecting the functional diversity of common species, and fast-acting potassium was a significant environmental factor affecting the functional diversity of rare species. Our results highlighted that although species-rich tropical forests had high probability of functional redundancy, the insurance effect provided by that could not offset functional vulnerability in the ecosystems. Reducing loss of species with unique trait combinations and occasional species is an effective and necessary way to avoid the loss of functions in tropical forest ecosystems.