Plant functional traits reflect the response of plants to environmental change. Understanding community assemblages and plant response to environmental change requires examining the variation in plant functional traits along environmental gradients, including the relationship among different traits. One important topic in ecological research is trait-gradient analysis used to explain relationships between plant traits and their environment.Plant functional traits have large variations in space. Understanding the variation patterns in functional traits and the correlations between different traits are the basis of adopting a trait-based approach. To understand how plant functional traits change across environmental gradients and plant trait variation within and among communities, we examined 32 vegetation plots in the Yanhe River basin, Shaanxi province. We measured two plant functional traits (leaf area and specific leaf area) of 98 species in these plots. We used trait-gradient analysis to reduce these two traits into α and β components, analyzing changes in species functional traits along environmental gradients using a combination of moisture and temperature, including the variation in plant traits within and among communities. The results showed that along the environmental gradient leaf area increased while specific leaf area decreased. Along the environmental gradient, species with larger leaves were represented more compared with smaller leaved species in the hilly loess region. Species gradually increased growth rates, reducing their nutrient-use-efficiency strategies to adapt to the environment. Among plant communities, using the β component of herb, shrub and tree communities, the species mean specific leaf area gradient was 2.56, 2.46 and 2.40. This indicated that species' specific leaf area increased in the order from tree-shrub-herb communities. In the Yanhe River basin, the niche breadth was 0.85, 0.73, and 0.5 for herb, shrub and tree communities, respectively. This finding suggests that herb and shrub communities were more widely distributed compared with tree communities. Within plant communities, the range of the α value was -0.857-1.578 and the range of the β value was 1.126-2.563, with the α value range wider compared with the β value range. This result suggests that the variation in plant species' specific leaf area, with respect to symbiotic species, was higher compared with the species community mean specific leaf area. Species mean leaf area and specific leaf area showed no correlation to environmental gradients. The α-component of species' specific leaf area and leaf area showed a non-significant correlation, while the β-component of species' specific leaf area and leaf area showed a significant correlation to environmental gradients. The dependence of the relationship between leaf area and specific leaf area within plant communities was stronger compared with those among symbiotic species. Species evolve different life-strategies to adapt to changing intra- and interspecific environments. Our findings provide an important guide for vegetation rehabilitation in the loess hilly region.