Abstract: It has been demonstrated that this canker is caused by Pseudovalsella sp., whose clonal name is Coryneum kunzei Corde var. castaneae Sacc. & Roum, and which is hiterto found in Southwest of China only. The fungus is a weak parasite. This article describes the bionornics of the pseudovalsella sp. and Coryneum kunzei var. castaneae. The optimum temperature of the germination is 30℃ for eonidia, 35℃ for ascospore, and the best relative humidity is 65%. Sugar solution, the extract of the host's bark, pH 4 or pH 8, naturally diffused light and some ultraviolet light are beneficial to the germination of conidia and ascospore.