Abstract: Background Caryopteris forrestii is a typical native shrub in the southeastern margin of the Qinghai-Tibet Plateau, with a well-developed root system, and contributes significantly to slope stabilization and the mitigation of soil erosion. Its rhizosphere soil bacterial community is closely related to plant growth, but systematic research on the distribution pattern of this community and its driving factors under different altitude gradients is still lacking. Methods In this study, 7 elevation gradients were set along the 2140–2750 m altitude range on the southeastern edge of the Qinghai-Tibet Plateau. The rhizosphere bacterial community structure and diversity of Caryopteris forrestii were characterized via 16S rRNA gene high-throughput sequencing, followed by an investigation into their environmental drivers based on soil physical and chemical properties. Results The results showed that the soil water content, pH, electrical conductivity, and organic carbon content of the rhizosphere soil of Caryopteris forrestii decreased significantly with increasing altitude, while the total phosphorus content showed a unimodal distribution along the altitude gradient. A total of 48 bacterial phyla and 114 bacterial classes were identified in the rhizosphere soil, with the dominant groups including Actinobacteriota, Acidobacteriota, Proteobacteria, Gemmatimonadota, and Chloroflexota. Among the α-diversity indices, the Shannon, Chao1, and ACE indices all increased significantly with increasing altitude (P < 0.05). β-diversity analysis revealed that the bacterial community structure differed significantly along the altitude gradient, with the most obvious separation between high and low altitudes, while the middle altitudes showed a higher degree of aggregation. Except for soil available phosphorus, soil water content, pH, organic carbon, electrical conductivity, total nitrogen, total phosphorus, and altitude all significantly affected the bacterial community structure (P < 0.05), among which soil pH and soil water content were the most critical driving factors. Different bacterial groups exhibited differentiated environmental adaptation strategies: Chloroflexota showed a significant positive correlation with pH, while Proteobacteria and Actinobacteriota showed significant positive and negative correlations with soil water content, respectively (P < 0.05). The structural equation model further revealed that the effect of altitude on the bacterial community structure was mainly a direct effect, with a certain indirect effect through influencing soil physicochemical properties. Conclusions This study clarifies the regulatory mechanism of altitude and soil environmental factors on the rhizosphere soil bacterial community of Caryopteris forrestii, identifies the key driving role of pH and water content, and provides theoretical support and practical reference for the subsequent use of Caryopteris forrestii in soil and water conservation and ecological restoration on the plateau.