Abstract: By use of the parasitological survey in Chongqing, Sichuan, Hubei, Hunan, Yunnan, Jiangsu, Zhejiang, Jiangxi, Gansu et al., and in combination with the previous research achievements, a probe was made into the diversity and flora distribution of ectoparasitic trichodinids on Cyprinidae fishes. The research result was that fifteen Cyprinidae fishes were found to be parasitized by thirty-nine trichodinid species subjected to three genera in the family of Trichodinidae. Based on the distribution characteristics of freshwater fishes in China, host fishes like Carassius auratus, Cyprinus carpio, Mylopharyngodon piceus, Ctenopharyngodon idellus, Hypophthalmichthys molitrix and Aristichthys nobilis were the most parasitized by trichodinids in all the Cyprinidae fishes. The result indicated that when compared with the wild Cyprinidae fishes, the diversity of trichodinids from the cultural ones was relatively abundant, and among those cultural Cyprinidae fishes, fishes which were cultured widely and in high density were found to be of a much more abundant diversity. Besides, the diversity of ectoparasitic trichodinids was markedly related to the flora distribution of Cyprinidae fishes in China.