Plant functional groups (PFGs) are defined as groups of species that either exhibit the similar responses to environmental perturbations or have the similar effects on major ecosystem processes. Discussing the functioning and stability-maintaining mechanisms of the terrestrial ecosystems, the adaptations and responses of plants to environmental changes, as well as water and nutrient use efficiency from the plant functional group perspective have become a major research approach in ecosystem ecology. PFGs analysis is an effective approach to reduce the complexity of plant communities and to reveal the general patterns and processes in the riparian zone ecosystems. The Yiluo River is an important tributary of the Yellow River in the south side of the middle reaches of the Yellow River. The vegetation in the riparian zone ecosystem of the Yiluo River has been heavily impacted by human. Although the species richness is high in this area, the herbs are mainly composed of a small number of dominant species whose abundance vary significantly among different types of landscape elements. Highly responsive to the changes in environmental conditions,herbaceous plants are very useful to the study of vegetation-environment dynamics. Using community ecology techniques, we investigated plant assemblages of the dominant herbaceous species in the riparian zone ecosystem of the Yiluo River. We calculated importance values, which were used to identify dominant species. Then we calculated the frequency of occurence and importance values of 27 species and identified dominant species. χ² test, together with association coefficient (AC) and percentage co-occurrence (PC), were used to measure interspecific associations of the dominant herbaceous species. PFGs were defined according to the interspecific associations and the distribution of landscape elements of the dominant herbaceous species of the herb layer. Dynamics of these PFGs along the moisture and original destination were analyzed. The results of this study showed that, classifying PFGs according to the dominant herbaceous species is feasible in the studies of herbs in the riparian zone ecosystem plant assemblages, and PFGs defined in this way are representative. Five PFGs, each with its unique spatial distribution and morphological characteristics, were identified: "widespread type", "wet type", "middle-xeric type", "farmland-escape type", and "invasion type". These PFTs appear to reflect vegetation-environment dynamics wel1. Taking Digitaria sanguinalis as an example, it is widely distributed in most habitat types of the riparian zone ecosystem. Therefore, we classified it as a widespread type. Alternanthera philoxeroides, with a strong adaptability and asexual reproduction ability, mainly distributed in the flood terrace shaping the film distribution pattern, is a typical invasive species. The same function group of species shows significant connection, occurring together more likely in the same habitat. In the long term growth evolution process, they can adapt to the similar resource and environment and have the similar responses to disturbance. Furthermore, due to the long term of natural and anthropogenic disturbance, together with the invasion of alien species, the biological diversity and ecological security of the riparian zone ecosystem in the Yiluo River is facing serious challenges. The problem of habitat fragmentation and biological invasion is serious in the Yiluo riparian ecosystems, and the local government should strengthen and improve the management of ecological safety.