Plant functional traits are important attributes that characterize plant adaptation to environmental changes as well as the evolution and balance of plant functions. The relationship between functional traits and environmental conditions is essential for understanding vegetation's adaptation strategies to the changing habitats. Three biogeographical and climatic zones (Steppe, Forest steppe, and Forest) in the Yanhe River Basin of the Loess Hilly Region were stratified sampled in this study, and the field experiments were performed to determine the functional traits of plant communities and the physicochemical characteristics of the soil. Changes in functional traits of plants along the vegetation zone and their responses to environmental conditions were analyzed in combination with meteorological data. The results are as follows:(1) the specific leaf area (SLA), leaf nitrogen content (LNC), leaf nitrogen-phosphorus ratio (LN/LP), root carbon content (RCC), root carbon-nitrogen ratio (RC/RN) and root nitrogen-phosphorus ratio (RN/RP) increased significantly from Steppe to Forest, while leaf tissue density (LTD), leaf carbon-phosphorus ratio (LC/LN) and specific root length (SRL) decreased significantly. The phosphorus content of plants in the Forest-steppe was significantly higher than that in the Forest and the Steppe. (2) Water conditions were the dominant factors regulating the variation of plant community functional traits, which could directly affect leaf and root functional traits, and indirectly affect leaf functional traits by influencing soil nutrients and moisture levels. (3) Plant communities could enhance the ability to adapt to dry and barren site circumstances by increasing SLA, decreasing LTD, and SRL as the availability of nutrients and water increased from the Steppe to the Forest. Nitrogen was the main limiting element for plant growth in Steppe areas, while Forest steppe areas were simultaneously limited by N and P.