Functional diversity is regarded as a key in understanding the link between ecosystem functioning and biodiversity. Quantifying the functional diversity in plant communities is very important for both studying the response of diversity to environmental change and the effects of diversity on ecosystem functioning. However, because the concept of functional diversity remain rather ambiguous, there are questions about how to define and measure it, how to evaluate the effects of it on ecosystem functioning. In this article, based on the review of the great deal of scientific literatures, which focus on plant communities, the definition and measurement of functional diverstiy were introduced. When quantify the functional diversity of plant communities, cares should be taken in the choice of various method such as how many and which traits to use according to its importance in plant growth and ecosystem functioning, how to weight them, how to quantify the species′relative abundances in a community, and how to interpret and predict changes of ecosystem processes by using it. This review will aid ecologists in examining the mechanisms controlling diversity-ecosystem functioning relationships