Understanding the effect of soil salinity on the diversity and species distribution of plant communities in inland salt marsh ecosystems could provide solutions for the management of regional saline soils and the protection of salt marsh wetland vegetation. A field experiment in succulent halophyte, Carex, and gramineous grass habitats in Ordos, Inner Mongolia (northwest China) was conducted to study the diversity and composition of plants in different saline habitats in inland salt marsh ecosystems. Results showed that plant diversity and species richness in the Carex habitat were significantly higher than the succulent halophyte habitat and the gramineous grass habitat (P < 0.05). Further, species abundance was higher in the succulent halophyte habitat and the Carex habitat than the gramineous grass habitat. Similar results were obtained when considering the abundance of constructive species. No significant differences in the abundance of dominant species and companion species between the gramineous grass habitat and the Carex habitat were found. We concluded that species abundance, species richness, species distribution, and plant diversity together explained the response of plant communities in different habitats to soil salinity, especially Na⁺ and SO₄²⁻. This highlights the importance of soil salinity for the maintenance of plant diversity and structural composition in inland salt marsh ecosystems.