Wetlands in the Lingnan region are rich in plant resources, exhibiting layering phenomena such as tree layer, herb layer, and aquatic plant layer, based on the space occupied by different plant communities in the vertical direction, where the herb layer primarily consists of native and invasive species that naturally grow in the understory, in high-density urban centers, the herb layer of wetlands experiences high levels of artificial interference, species diversity is reduced, and the invasion of foreign species is serious and other phenomena. Studying the ecological niche characteristics of wetland herbaceous layer provides important insights for mega urban wetlands to achieve low-maintenance management and enhance the heterogeneity of urban habitats. Xiaozhou and Zuitou wetlands, located on either side of the Guanzhou waterway in central Guangzhou, were selected as the study subjects. A total of 162 wetland herbaceous layer sampling plots were selected by grid system sampling method to quantitatively analyze and compare the niche width and niche overlap of their dominant species by using the methods of Levins niche width and Pianka niche overlap index. The results showed that: (1) The competition in the herbaceous layer of the wetlands in the study area is intense, and the number of invasive species is less than that of the native species, but the importance value and niche width are higher, in which the largest invasive species in the two wetlands are Sphagneticola trilobata, Paspalum conjugatum, etc, which have caused a gradual decrease in the niche width of the native species by squeezing the living space of native species; the native species with the highest importance value is Commelina communis, which is better adapted under the state of no artificial intervention for a long period of time. (2) There is no obvious positive correlation between the importance value and the niche width. Factors affecting the niche width include the importance value, frequency of distribution, space and environment. (3) The niche overlap between invasive species and native species was common, and the overlap between each other was more significant than that between invasive plants and native plants. The overall average ecotone width and ecotone overlap value of the herbaceous layer in the Zuitou Wetland were greater than those in the Xiaozhou Wetland, and the competitive exclusion between species in the wetland was stronger, and the growth of autochthonous native plants was at a relative disadvantage. (4) The herb layer community in Xiaozhou Wetland was more stable than in Zuitou Wetland, suggesting that natural succession in the herb layer, with appropriate artificial intervention, could enhance species diversity by fostering a more balanced interspecific relationship among native species, which could help to build a relatively stable herb layer plant community in the vernacular wetland. The results of this study can be used as a reference for the prevention of invasive plants, the optimization of wetland herbaceous layer structure, and low maintenance management in high-density urban center environments.