In order to research anthracnose of Dendrobium officinale, symptoms observation, isolation and culture, pathogenic fungus identification and pathogenicity test were carried out in both laboratory and cultivation field respectively. The results showed that Colletotrichum dematium only damage leaf, the average incidence was 11.3%. C. dematium accounted for 44.1% among of the isolated 59 fungal colony. The research confirms that pathogenic fungus caused by D. officinale anthracnose was C. dematium after morphological description, DNA sequencing to identify and pathogenicity test. C. dematium is the first reported pathogenic fungus on D. officinale in China.