Fine roots are the main organs that plants use to absorb water and nutrients. In the context of global warming, it is of great significance to study the biomass of fine roots and the environmental factors affecting carbon balance, carbon budget, and contribution rate of the ecosystem. In this study, the soil drilling method and indoor analysis were used to determine the fine root biomass and soil physical and chemical properties of 5 species in forest system on 6 elevations in Qinghai Province. The relationships between fine root biomass and environmental factors were further analyzed. The results showed that:(1) In Qinghai Province, the average of the total fine root biomass was 8.50 t/hm² in 0-40 cm soil depth. With the altitude increase along the gradient, fine root biomass decreased first and then increased. There were significant differences in the biomass of fine roots among different altitudes (P < 0.05), and the highest peak of fine root biomass appeared at 2100-2400 m. (2) The total fine root biomass of 5 forest species in the 0-40 cm depth was as follows:Betula platyphylla < Populus tomentosa < Picea asperata < Sabina chinensis < Populus davidiana. There were no significant differences in biomass of fine roots among different stands. (3) Fine root biomass decreased with the soil depth, and 70% of the fine roots were concentrated in 0-20 cm soil layer. (4) Soil bulk density in the 20-40 cm soil layer was significantly greater than that in the 0-20 cm soil layer (P < 0.05). It increased with the altitude, and there were substantial differences among the 5 forest species. (5) The contents of total carbon (TC), total nitrogen (TN) and total phosphorus (TP) in the surface soils (0-20 cm) were significantly higher than those in the deeper soils (20-40 cm). TC and TN increased first and then decreased, while TP decreased with the altitude gradient. The differences in soil nutrients between different forest species were obvious. (6) SEM analysis showed that the fine root biomass was significantly correlated with altitude, soil layer, and bulk density, and the biomass of fine roots directly affected soil nutrients. The forest species affected the fine root biomass indirectly. Therefore, the plant species and elevation affected the biomass and spatial distribution of fine roots by influencing the soil micro-environment.