Abstract:Orchidaceae is the second largest family of flowering plants. There are 28 000 species in 736 genera identified, among them, 343 species in 82 genera are used as medicine, such as Dendrobium officinale, Gastrodia elata, Bletilla striata, Anoectochilus roxburghii, and so on. The main functional constituents in medicinal Orchidaceae plants are polysaccharides, stilbene derivatives, phenolics, terpenoids, alkaloids, flavones and sterols. Water-soluble polysaccharide in orchid plant are mainly composed of mannose and glucose, which is one of important pharmacological active constituents with many pharmacological functions, such as enhancing immunity, anti-tumor, anti-oxidation, lowering blood glucose and improving memory. The structure, pharmacological function and biosynthesis of active polysaccharide in medicinal Orchidaceae plants are reviewed, and some key problems were proposed for further research, which would provide references for further promoting the protection and rational exploitation of medicinal resources of Orchidaceae.