Patterns and determinants of species richness are the central issues in ecology, but there is still a lack of consensus on their formation mechanisms. In order to explore the distribution patterns and determinants of community diversity along lakeshore-highland environmental gradient (local scale) in western Songnen Plain semi-arid region, species richness, α diversity, β diversity and environmental factors including water level (WL), soil water content (WC), organic matter (OM), etc. were measured by setting up sample belts and cluster analysis in seven communities (Typha angustifolia wetland, Typha minima wetland, Phragmites australis wetland, hassock wetland, Calamagrostis epigeios meadow, Leymus chinensis meadow and elm sparse forest) along this gradient, to reveal the spatial variation and formation mechanisms of community diversity. The results show that, along lakeshore-highland environmental gradient:(1) both species richness (2.00-18.00) and α diversity (Simpson index 0.12-0.90; Shannon-Wiener index 0.23-2.57 and Pielou index 0.34-0.88) showed a similar N-shaped distribution pattern (Typha angustifolia wetland was the lowest at the lower deep-water habitats, hassock wetland was the highest at the lower-middle seasonal inundated habitat, the lower at the middle-upper wet habitats of Calamagrostis epigeios meadow and the higher at the upper arid habitats of dune elm sparse forest). (2) We partitioned the generalized β diversity (Jaccard index 0.56-0.96) into two components:species turnover (species replacement among sites without changes in richness) and nestedness (species differences among sites when species-poor sites constitute subsets of those with a greater number of taxa). β diversity was relatively high at arid habitats located in upper half and shallow-water habitat located in lower half of the gradient, and it was mainly controlled by turnover processes. At the permanently inundated habitats, it was the lowest one, which is controlled only by nestedness processes. But in the middle of the environmental gradient, the turnover and nestedness processes control it togther. (3) The main controlling factors of species richness and α diversity were significantly converted along the gradient. The high water level area was jointly controlled by water level, organic matter and total phosphorus (TP), the medium water level area was controlled only by available phosphorus (AP) and the low water level area was jointly controlled by pH and water content. Therefore, there were obviously spatial distribution patterns of species richness and α diversity, and higher β diversity along lakeshore-highland environmental gradient in the Songnen Plain semi-arid region. Our results suggested that the main mechanism was the interaction between the local spatial environmental heterogeneity created by microtopography and the region species pool, which jointly shaped the plant community diversity. Thus, its spatial distribution patterns integrity should be protected in the practice of biodiversity management.