Functional traits vary with vegetation types, but it is not clear how multidimensional functional spaces composed of functional traits adapt to natural forest plant communities, especially at the soil microenvironmental scale. To investigate the effects of soil factors on the functional diversity of forest ecosystems, functional trait spaces of 45 plant communities at three areas in the Tianshan Mountains were analyzed. The results show that as longitude increases, soils become relatively infertile and hydrothermal conditions become unfavorable. For the functional spaces, the functional richness (FRic) and evenness (FEve) across vegetation types is Mixed Forests > Broadleaf Forests > Coniferous Forests > Shrubs > Herbs, whereas functional divergence (FDiv) between vegetation types do not vary significantly. The spatial range of functional spaces expands with soil nutrient and water content, while the functional evenness and divergence are significantly correlated with slope and soil temperature. The total functional beta-diversity has a similar trend to its beta-nest component, with the maximum value found in the forest-herb assemblage (0.3052-0.5787), suggesting that forests and herbs possess different ecological functions and different growth strategies. The mixed forests-shrub assemblage has the minimum beta-nest component (0.0343) and the maximum beta-turnover component (0.8484). And the most important factors affecting vegetation functional diversity are soil nutrient content, soil water content and soil temperature.