This study investigated the impact of Bacillus subtilis on plant growth and the rhizosphere microbial community in rose cultivation under saline–alkaline stress. Saline–alkaline stress was simulated with varying salt and alkali levels. Bacillus subtilis was introduced, and 16S rRNA high-throughput sequencing was conducted to analyze the root microbial community. Introduction of Bacillus subtilis significantly promoted rose growth and mitigated saline–alkaline stress effects. Gene sequencing revealed increased abundance of microbial genera, such as Tessaracoccus, Intrasporangium, Glutamicibacter, Agrobacterium, Saccharibacteria, Falsochrobactrum, Mesorhizobium, Bacillus, Ensifer, and Ornithinicoccus, under normal and saline–alkaline conditions, while functional changes in colony abundance were observed under different environments through PICRUST2 analysis. Bacillus subtilis demonstrated potential in enhancing rose growth and stress resistance under saline–alkaline conditions, affecting the regulation of the root microbial community. This study provides insights for improving soil conditions and enhancing plant adaptability in saline–alkaline regions.