Abstract: Environmental characteristics, spatial heterogeneity, and biological interactions are key factors that affect ecological communities. We studied how environmental factors and spatial patterns influence the structure of Stipa breviflora communities in the Inner Mongolia region. First, we used the two-way indicator species analysis (TWINSPAN) algorithm to summarize variation in species composition and group 202 study plots. Second, we investigated the effects of three environmental and three spatial factors, together with their interaction, on the structure of S. breviflora communities by using detrended canonical correspondence analysis (DCCA). 1) The target plant communities were classified into 16 groups at the fourth level of division by TWINSPAN; 2) The first two DCCA axes, which corresponded to gradients of temperature and precipitation, respectively, explained most of the variation in community structure (75.3%). Based on these results different S. breviflora communities were arranged into an ecological series; 3) When analysed together, 70.7% of the total variance in S. breviflora community structure was explained by all environmental factors and 55.6% by all spatial factors. When these factors were examined separately, only 29.5% and 11.4% of the total variance were explained respectively, while 44.2% was simultaneously explained by the two groups of factors, and 17.9% was explained by other undetermined factors. Our study contributes to other researchers’ findings and strongly supports the conclusion that the degree to which environmental factors control the structure and spatial distribution of plant communities is determined by complexity of the vegetation pattern. The explanatory power of plant community structure by environmental factors decreases with the increase in complexity of vegetation cover.