Plant epicuticular wax is a collective term used to describe the organic components of the cuticle which covers the outer surface of aerial plant tissues. It is also the last defensive barrier of plant, playing important roles in plant growth and development. The components, transport, crystal formation and morpho-ultrastructure of plant epicuticular wax as well as the investigations concerning the relationship between epicuticular wax and adaptations to environment are reviewed. Especially, we systematically summarized the relationships among wax, cutin transpiration, leaf WUE and yield and the progresses in the physiological and molecular biology research regarding wax; we also discussed the problems existing in wax research.