Taking Bayanbulak alpine grassland on the southern slope of Tianshan Mountain, Xinjiang as test object, the relationships between belowground biomass and environmental factors along an altitude gradient were analyzed. The results showed that with increasing altitude, the belowground biomass of alpine steppe dominated by Stipa purpurea and Festuca ovina, alpine steppe meadow dominated by Kobresia capillifolia and S. purpurea, and alpine meadow dominated by Carex stenocarpa, Alchemilla tianschanica, and K. capillifolia all increased gradually. There was a significant positive correlation between altitude and belowground biomass (P<0.01). The belowground biomass decreased with soil deep and with a ‘T’ shape distribution. In alpine steppe, alpine steppe meadow, and alpine meadow, the belowground biomass in 0-10 cm soil layer occupied 68.1%, 84.1% and 86.7% of the total, respectively. The belowground biomass of the alpine grassland was negatively correlated with air temperature and positively correlated with relative humidity and soil water content (P<0.01), but had no significant correlation with soil organic matter, available nitrogen, and pH value.