Abstract: Based on measure formula of species diversity, the plant species and composition characteristics of herbage and shrub communities in floodplains wetland of suburb of Xichengyi of Ganzhou District of Zhangye City in Heihe River basin were investigated. The results showed that Phragmites communis was the dominant species of the herbage community, and the important value was 24.16. Typha minima was the dominant species of shrub community, and the important value was 47.54. The results of species diversity analysis of the two communities showed the consistent trends that the diversity index values were relatively lower. Furthermore, the abundance degree, Simpson diversity index, Shannon-Wiener index and uniformity index of shrub community were all higher than those of herbage community, whereas the dominant index of shrub community were higher than that of herbage community. The results of variance analysis showed that there were no significant differences of species diversity index between the two communities, indicating that the structure of the two communities had not obvious changes. It was indicated that the plant structure of the investigated communities were simple and the plant diversity were low, whereas the advantage phenomenon were serious.