High-altitude stream ecosystems are sensitive to environment disturbance, and thusare considered as excellent indicators of environmental changes and human disturbance. This study focused on the Tianquan River, a representative subtropical high-mountain stream situated at Tianquan County, Sichuan Province. Surveys were carried out at 20 sampling sites along the upper reaches of the Tianquan River in April and October 2018. The aim of this study was to explore the spatio-temporal patterns and driving processes of taxonomic, functional and phylogenetic alpha diversity of benthic macroinvertebrates in the undisturbed high-mountain streams. Specifically, it sought to identify the key environmental and spatial factors influencing diversity, along with the relative contributions of the two sets of explanatory variables. Distance-based linear models analysis showed that significant environmental factors affecting taxonomic diversities were altitude and velocity, whereas the significant spatial factors were PCNM 4-6 based on overland distance. The functional diversity indices responded significantly to substrate type and turbidity (environmental factors), and overland distance-based PCNM 6-8 and watercourse distance-based PCNM 3 (spatial factors). Only environmental factors (altitude and substrate type) significantly influenced phylogenetic diversity indices. Variation partitioning analysis indicated that the pure contributions of environmental factors (0.6%-21.5%) and spatial factors (0.2%-16.6%) accounted for similar amounts of variation in taxonomic and functional diversity indices, highlighting the significant roles of both sets of factors. The variation in phylogenetic diversity were better explained by environmental factors (12.1%-23.3%) than that explained by spatial factors (0-6.9%), highlighting the dominant role of environmental factors. This study unveiled the diversity patterns and driving mechanisms of macroinvertebrates in the upper reaches of the Tianquan River, offering crucial theoretical groundwork for comprehending the diversity status, management, and conservation of subtropical high-mountain stream ecosystems.