Abstract: The distribution of the endangered aquatic fern Ceratopteris pteridoides at Hubei Chilong Lake National Wetland Park in China was investigated. The relationship between its distribution and water quality was analyzed. We studied the population characteristics of Ceratopteris pteridoides using Braun- Blanquet′ s method and visual method. The results showed that Ceratopteris pteridoides was mainly found in lake branches，ponds and ditches at Shajing village，Shijiatang，Xiamiao village and Suwei village of the Wetland Park. The population area，number and coverage of four Ceratopteris pteridoides populations were significant different，and their abundance were smaller. It was found that 13 aquatic plant species belonging to 12 families and 11 genera in the community. Nitrate nitrogen（NO₃^--N）and total phosphorus（P）in the main lake（Hengfeng Lake）of Chilong Lake was 0. 4 mg/L and 0. 2 mg/L，indicating the main lake is eutrophication. Human activity such as excessive breeding and the deterioration of water quality might be the main factor responsible for the extinction of the species.

Key words: Chilong Lake, wetland park, Ceratopteris pteridoides, distribution；endanger