To identify the key roles and underlying mechanism for assembling soil microbial community structures at regional scales, we examined soil bacterial community compositions from 20 locations in a transect of grasslands of southern China. The bacterial community was sequenced for microbial 16S ribosomal RNA gene amplicons using Illumina MiSeq technology. The soil microbial community diversity was analyzed for plant, soil, geographic properties, and pure spatial distance based on a distance-based approach and with variation partitioning based on canonical redundancy analysis. The soil bacteria richness and alpha diversity index showed marginal positive relationship with plant richness and Shannon index. The bacterial community compositions of both the taxonomic and phylogenetic structures were best explained by the soil pH and plant diversity and soil nutrient availability, with the peak richness at pH 6.8. While the plant, soil and geographic factors were correlated with bacteria community dissimilarity, soil pH and plant diversity, nitrogen availability were relatively independent dominant community assemblage by quantifying taxonomic and phylogenetic turnover. Mantel tests indicated the assembly of soil bacterial community was predominated by the determinant processes. Overall, our findings suggest plant functional traits and abiotic soil properties (e.g., soil pH and inorganic nitrogen) collectively drive soil bacterial diversity patterns but are not limited by pure spatial distance in grasslands of southern China.