The species diversity is an important trait of plant ecological adaptive strategy. The plant community of riparian zone along Taizi River plays an important role in the stabilization of plant composite. However, the species diversity of riparian zone along Taizi River is quite poorly known. The objectives are to investigate the species diversity of the understory of riparian zone along Taizi River in order to provide the theory of ecological restoration and technical basis. The diversity of plant species in 23 plots of the zone is investigated by calculating the indices of species diversity, richness, evenness, and dominance from important values. The results indicate that there are 201 species of plants belonging to 36 families and 124 genera in the 23 plots of riparian zone along Taizi River. The species composition of the community is relatively rich, but all are confined to herbaceous plant. The main families are dominated by the Compositae, Gramineae, Polygonaceae, Cyperaceae, and Rosaceae. The compositions of the community are concentrated, and the plant species give first place to Juncus effusus L., Beckmannia syzigachne (Steud.) Fern., Polygonum hydropiper L. angustifolium A. Br., Echinochloa crusgalli (L.) Beauv., Alopecurus aequalis Sobol., Polygonum hydropiper L., Rumex acetosa L., Artemisia adamsii Bess., Carex dispalata Boott ex A. Gray, Zoysia sinica Hance, Poa subfastigiata Trin., Scirpus orientalis Ohwi, etc. The community structure of riparian zone along Taizi River is simple in studied area. The ecosystem is deteriorating with richness indexes changing between 3.00—28.00, Pielou indexes changing between 0.66—0.89, Simpson indexes changing between 0.54—0.91, Shannon-wiener indexes changing between 0.86—2.73, Simpson dominance indexes changing between 0.09—0.46. The riparian zone along Taizi River is disturbed by human activities, such as agricultural production, dredging, and other human activities that result in the reduction of the level of community diversity.