Abstract: The community structure of meadow steppes and typical steppes in the Hulun Lake Basin has undergone significant changes under the combined impacts of climate fluctuations and anthropogenic disturbances. However, the response mechanisms of species diversity to environmental factors across different grassland types remain unclear. Based on field vegetation surveys and meteorological data for the 2022-2024 growing seasons, this study employed correlation analysis and structural equation modeling (SEM) to explore the dynamic changes in community characteristics and their responses to environmental drivers in meadow and typical steppes in the Hulun Lake Basin. The results indicated that: Species diversity was higher in the meadow steppes than in the typical steppes, yet both exhibited a declining trend during the observation period. From 2022 to 2024, aboveground biomass decreased by 42% and 79%, respectively, with annual vegetation cover declines reaching 16% and 22%. The diversity indices of the typical steppe showed different interannual patterns: the Shannon–Wiener and Patrick richness indices first increased and then decreased, whereas the Simpson and Pielou’s evenness indices first decreased and then increased. Overall, the diversity level remained lower than that of the meadow steppe. SEM revealed that at the grassland-type scale, the meadow steppes were more sensitive to short-term meteorological fluctuations, whereas the typical steppes relied more heavily on underlying soil moisture and temperature conditions. Temporally, long-term soil properties provided the foundation for grassland stability; however, under extreme climatic fluctuations, the short-term dominance of meteorological factors could mask this underlying soil support. Grassland diversity exerted a significant negative effect on aboveground biomass. Under drought and grazing stresses, the colonization of short, drought-tolerant weeds temporarily increased species diversity, but this shift could not compensate for the productivity decline caused by the degradation of dominant forage grasses. These findings highlight the extreme vulnerability of arid and semi-arid grasslands to severe interannual environmental shocks, providing a scientific basis for the conservation and management of grassland ecosystems of the Hulun Lake Basin.