Aquatic plants are an important part of wetland ecosystems. Studies about the distribution pattern of aquatic plants and its influencing factors can provide important background for the regional protection of aquatic plant resources. In this study, the main aquatic plant community types, quantitative characteristics, species richness patterns, and influencing factors of aquatic plants in the Hexi Corridor were studied using field investigation data. The mid-domain effect hypothesis was used to explain geographical diversity patterns of aquatic macrophytes in the region. The main results are as follows:(1) there were 84 species belonging to 42 genera of 29 families of aquatic plants in the Hexi Corridor. Cluster analysis of the community showed that there were 15 main aquatic plant community types in this region; (2) the aquatic plant community types in the Hexi Corridor were mainly affected by environmental factors such as water temperature, elevation, latitude, and longitude. The community species diversity index was significantly correlated with salinity and total dissolved solids; (3) the spatial pattern of aquatic plant diversity in the Hexi Corridor exhibited a unimodal pattern. The mid-domain effect model better explained the latitudinal pattern and the vertical distribution pattern of aquatic plant diversity in the region, with explanation rates reaching 57.56% and 63.5%, respectively. These results indicate that the patterns of aquatic macrophyte species richness in the Hexi Corridor were determined by geometric (boundary) constraints, random processes, and other unknown processes. Geometric (boundary) constraints and random process showed a higher contribution rate on geographic richness gradients. Also, we highlight that unmeasured factors including environmental heterogeneity, climate, and human disturbance may greatly affect aquatic plant species richness in the Hexi Corridor of Northwest China.