Stomata are the valves for water and CO₂ exchange between plants and the surrounding environment, regulating plant transpiration as well as photosynthesis to some extent. Therefore, the spatial variation of stomatal traits affects plant functions and reflects the adaptation of plants to their environments. The stomatal traits have attracted scientists' attention for a long time. However, spatial variation in the stomatal traits of grassland plants on the Inner Mongolia Plateau and their responses to the environment has not yet been explored. In this study, we set up 10 study sites, with low levels of human disturbance, along the precipitation gradient on the Inner Mongolian Plateau. In 2018, we collected nearly all the plant species that were present within a 1 km×1 km area of each site. The stomatal density (SD), stomatal size (SS), and the stomatal relative area (SRA) of the adaxial and abaxial epidermis of each species were measured. Meanwhile, the ratio of stomatal traits between the abaxial and adaxial epidermis was calculated. Results showed that the mean SD, SS, and the SRA were 262.29 stomata/mm², 378.84 μm², and 8.10%, respectively. The mean stomatal density ratio (R.SD), the stomatal size ratio (R.SS), and the stomatal relative area ratio (R.SRA) were 1.54, 1.04, and 1.61, respectively. Due to the open grassland habitat, there were no significant differences in leaf stomatal morphological traits among the different life forms, namely herbs vs woody plants and annual or biennial herbs vs perennial herbs (P>0.05). With the increase in the degree of drought, the leaf SD and SRA decreased, and the SS increased. The mean annual precipitation was the main driving factor of stomatal variation, and the mean annual temperature and photosynthetically active radiation had no significant effect on stomatal traits. The SRA was mainly driven by the SD, and it was one of the most important mechanisms of reducing leaf SD to improve the drought tolerance of grassland plants on the Inner Mongolian Plateau. Plants can also adapt to drought by reducing the stomatal ratio. The stomata in the abaxial epidermic were the main contributor to the decrease in the stomatal ratio on the Inner Mongolian Plateau. These new findings help us further understand the unique climate adaptation mechanisms of plant stomata in natural grassland communities and provide these ecological process models as baseline data.