It is indispensable to investigate species diversity for maintaining the integrity of riparian ecosystems. In this study, integrating the BraunBlanquet coverabundance scale and the quadrat sampling methods, we investigated diversity characteristics of plant community in typical river riparian zones in the middle and lower reaches of Yellow River, and analyzed the relationship between herbaceous plant diversity and environmental factors. The results showed that a total of 36 families, 78 genera, and 86 plant species were observed from 52 community quadrats in the study area. Plant community species composition was rather rich, while dominant species was not obvious. In a single community quadrat, species composition was simple. However, obvious difference existed between different quadrats regarding species composition and diversity. Moreover, species diversity was relatively low for the middle stream areas that were disturbed seriously by human activities, indicating that plant species diversity in the study areas was influenced seriously by habitat fragmentation caused by human disturbance. Redundancy analysis showed that altitude and distance to river were important factors influencing plant diversity of riparian zones in the middle and lower reaches of Yellow River.