【Objective】 As indicators reflecting soil fertility and biological activity, the soil microbial community plays key roles in global biogeochemical cycles by participating in litter decomposition and nutrient mineralization. The soil microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), and microbial biomass phosphorus (MBP) are labile and available nutrients for plants, and important for maintaining ecosystem functions. However, there is still a lack of information on the spatial distribution of the soil microbial biomass and the potential key drivers affecting it in the alpine meadows of Northwest Sichuan Province. Therefore, the current study aims to investigate the spatial heterogeneity of soil microbial biomass in the alpine meadows of Northwest Sichuan and its influencing factors based on the Second Comprehensive Scientific Expedition to the Qinghai-Tibet Plateau project. 【Method】 The typical alpine meadows in Northwestern Sichuan were investigated in this study to determine soil MBC, MBN and MBP by chloroform fumigation method. Soil pH, water content, total carbon, total nitrogen and total phosphorous were also measured. 【Result】 The results showed that (1) The content of MBC and MBN showed a decreasing trend from South to North alpine meadow in the Northwest Sichuan Province. Conversely, the MBP content showed an increasing trend from South to North while the MBC: MBN ratio showed a decreasing trend from Northeast to Southwest. Nevertheless, the MBC: MBP ratio was more complex and showed an overall decreasing trend from South to North while the MBN: MBP ratio showed an increasing trend from West to East.; (2) Random forest modeling results showed that mean annual temperature (MAT), mean annual precipitation (MAP), soil pH, and soil moisture (SMC) were important factors that positively affected soil microbial biomass and its stoichiometric ratio. The structural equation modeling (SEM) results further showed that soil pH and soil bulk density (BD) had direct negative effects on the changes of soil microbial carbon, nitrogen and phosphorous biomass whereas the stoichiometric ratio and soil total carbon (TC) had direct positive effects on them. MAT and MAP indirectly and negatively affected soil MBC, MBN, MBP, and the stoichiometric ratio, which was mainly attributed to the effects of MAT and MAP on soil physicochemical properties. Specifically, MAT and MAP increased both MBC and MBP mainly by lowering soil pH, and MAT also directly decreased TC, which increases MBN as well as decreased MBP; (3) Generally, the soil nutrients are limited in the alpine meadows of Northwest Sichuan Province, and showed the following trend: carbon > nitrogen > phosphorus. 【Conclusion】 Soil pH, BD, and TC had direct effects on the alteration of soil microbial biomass and its stoichiometric ratios in the alpine meadows of Northwest Sichuan Province, while MAT and MAP indirectly affected the soil microbial biomass and its stoichiometric ratios. In addition, the latitude and longitude showed effects on the spatial distribution pattern of nutrient limitation in the study area.