In this paper, Fourier transform infrared spectroscopy (FTIR) was used to compare the five dendrobium species' infrared absorption spectra of stem powder. The stem of Dendrobium is rich in saccharides. The saccharides of Dendrobium Officinale, Dendrobium Paxt and Dendrobium wardianum Warner are complex in composition. And the sugar units are mainly galactopyranose, grape pyranose, mannopyranose, arabinopyranose and xypyranose. The sugar components in the stem of Dendrobium strongylanthum Rchb. f. were simple. The sugar units were galactopyranose, grape pyranose and mannopyranose. Dendrobium wardianum Warner had the same chemical structure as Dendrobium strongylanthum Rchb. Dendrobium Officinale had the same chemical structure as Dendrobium devonianum Paxt. The species of Dendrobium could be identified by the characteristic absorption peak of the polysaccharide fingerprint absorption region.