Objective To study the spatial pattern and gradient variation of herb species , and then to understand the ecological adapatability of plants,so as to provide data for further understanding and maintaining the biodiversity in water-level-fluctuation zone.

Method Based on survey of water-level-fluctuation site of Zigui Section of the Three Gorges Reservoir Area, the composition and plant community diversity of herbaceous species and their spatial pattern and gradient variation were investigated continuously from 2014 to 2019 on the transect with elevation 145-175 m above sea-level .

Result The results showed that there were 39 herb species in total in 2014, belonging to 27 genera of 15 families. Gramineae, Compositae, Polygonaceae and Euphorbiaceae were the dominant families. There were 47 herb species belonging to 39 genera of 18 families in the water-level-fluctuation zone in 2019. The top dominant family was Compositae, followed by Gramineae, Euphorbiaceae, and Polygonaceae. The dominant species such as Digitaria sanguinalis, Setaria viridis, Echinochloa crusgalli, Xanthium sibiricum, Bidens pilosa, Cynodon dactylon, Cyperus rotundus were of high importance value over the five years. In addition, there was an obvious variation in species richness, community diversity, evenness and dominance along the distance gradient. The richness of community species followed a up-down trend on the elevation from 145 to 175 m above sea-level.

Conclusion The results of study suggests that the variation of herb species diversity in the study area is originated from the habitat difference induced by the difference in the flooding time caused by different elevation.