Soil diazotrophs possess the function of fixing atmospheric NZ into biologically available ammonium in terrestrial ecosystems. However, there are limited studies into how diazotrophic communities change when grassland environments differ. In this study, we elucidated the diversity and interactions of diazotrophic communities in three steppe types of Inner Mongolia, China, including non-desert steppe (MT), desert steppe (D) and sandy steppe (S). We expected to improve the predictions of diazotrophic responses to grassland degradation at time gradients based on their discrepancies among steppe types along spatial gradients. Steppe types affected the alpha- and beta-diversity of diazotrophic communities, which were mainly controlled by plant biomass and soil pH, respectively. Diazotrophic communities were strongly aggregated with their respective steppe environments, but dissimilar under different types according to Bray-Curtis distance. In addition, network analysis showed that the network structure of diazotrophs from the D was relatively simpler than the other two types (MT and S). More exclusionary relationships in diazotrophic communities occurred in the D and S steppes than in the MT steppe. The species shared across the steppes changed their interactions with other species to adapt to different habitats. Moreover, different steppes had distinct key species to underpin the whole network. The disturbances or extinctions of these key species may lead to the instability of the diazotrophic co-occurrence network. Overall, we speculate that if grassland degradation happens, the change of grassland microenvironment may mediate the differences in the diversity and co-occurrence patterns of diazotrophs, allowing them to adapt to environmental changes.