Abstract: Reservoir impoundment affects local climate. The soil microbes are a sensitive indicator for environmental changes and their response to dam development is rarely investigated. This study investigated the soil microbial in April and September in four reservoir zone: Xiluodu, Xiangjiaba, Baihetan, and Wudongde in the lower Jinsha River. The total PLFA content and soil microbial community in April and September in the reservoir areas of the dry-hot valleys were determined by the phospholipid fatty acid (PLFA) method. This study analyzed the dominant factors of soil microbial variations and quantified the effects of river interception and reservoir impoundment on the soil microbial community. The results showed that： (1) meteorological factors and soil nutrients could explain most of the variation of soil microbes, with the degree of explanation of Baihetan and Wudongde reservoirs (84.1%, 93.5%) larger than Xiangjiaba and Xiluodu reservoirs (41.1%, 77.0%). (2) soil microbes positively correlated with total nitrogen, available nitrogen, and precipitation in April, and negatively correlated with temperature and potential evapotranspiration. In September, soil microbes positively correlated with precipitation, organic matter, and available nitrogen, and negatively correlated with potential evapotranspiration.(3) the individual contribution of water impoundment to soil microbial variation in April and September was 2.2% and 6.8%, respectively, and the variation explained by both impoundment and other factors less than 22.4%. In contrast, in the Baihetan and Wudongde reservoirs, the individual contribution of the impoundment to soil microbial variation in April and September was 5.5% and 8.3%, respectively, and the joint contribution with other factors was 13% in both cases. Overall, impoundment caused by the hydropower development in the lower Jinsha River in hot-dry valleys affects soil microbial PLFA content and their community structure, but their effects are easily masked by climate change and soil properties. The impoundment in the cascade reservoirs, to some extent, moderates the adverse effects of typical hot and dry climate on soil microorganisms and improve the stability of soil microbial community structure. This study contributes to an in-depth understanding of the response of soil microorganisms to hydropower development and is important for the scientific assessment of the terrestrial ecosystem impacts of hydropower development and soil sustainability.