The relationship between plant diversity and plant competition intensity and niche overlap varies with the environment. To explore this relationship in Zoige, this study investigated typical aquatic, wet, wet-mesic, and mesic plant communities in Zoige in August, 2021. A new method for calculating plant competition intensity (CI) was constructed, and niche overlap of species (NOS) and species diversity indices (including species richness, Shannon-Weiner index, Simpson index, and Pielou index) were also calculated based on field data. Changes in plant diversity indices, CI, NOS, and relationships between these indices were then analysed across the habitat gradient. The results showed that:1) all plant diversity indices tended to increase from aquatic to mesic habitats (P<0.05). 2) The CI of wet-mesic habitat was significantly higher than that of wet habitat (P<0.05). The NOS of wet habitat was higher than that of aquatic habitat (P<0.05). The CI was not significantly correlated with NOS across the habitat gradient (P>0.05), but the two were inverted parabolic in wet habitat (P<0.05). 3) Plant community species richness was parabolic with CI (P<0.05), and the remaining three diversity indices were linearly and positively correlated with NOS across the habitat gradient (P<0.05). In terms of individual habitats, the Simpson, Shannon-Weiner, and Pielou indices were linearly negatively correlated with CI in wet-mesic habitat (P<0.05), but these indices were not correlated with CI in aquatic, wet, and mesic habitats (P>0.05). None of these four diversity indices, i.e. species richness, Simpson index, Shannon-Weiner index, and Pielou index, correlated with NOS in any individual habitat (P>0.05). These results suggest that plant diversity in Zoige tends to increase from aquatic to mesic habitats, but the relationship between plant diversity and species competition and niche overlap is complex. The results contribute to the understanding of the mechanisms that shape plant diversity in the Zoige plateau.