Exploring the structure and diversity distribution pattern of plant communities in the river corridor of the dry section of Yongding River can provide scientific theoretical basis for the construction of shelter forest and water conservation forest in Yongding River. The research quantitatively classified 124 plant communities by TWINSPAN based on the field survey of plant communities in the river corridor, and explored the differences of species diversity among different levels and the distribution patterns on vertical and horizontal gradients. The results show that: (1) the plant communities include 9 cluster types, among which the dominant clusters are Salsola collina + Chenopodium acuminatum cluster, Setaria viridis association and Populus×canadensis -Setaria viridis + Tribulus terrester cluster. (2) The richness and evenness of species in herbaceous layer are greater than that in arbor layer as a whole, and the complexity of species composition changes more greatly. (3) From the vertical gradient, the species composition of the arbor layer in plant communities is richer in the upstream than that in the downstream, and the overall distribution is more uniform. The richness and evenness of species composition in herb layer from upstream to downstream decreased first, then increased, and finally decreased. From the horizontal gradient, the closer to the Left Levee and Right Levee, the richer and more uniform the species composition of tree layer, and the more complex and more uniform the species composition of Left Levee compared with the Right Levee. The species diversity of herbaceous layer varies greatly on the horizontal gradient, and the species composition is most abundant near Left levee. The main reason for the change of species diversity in arbor layer is the intensity of human activities interference.