Leaf and fine roots are the most vigorous components of terrestrial ecosystems. Functional traits of leaf and fine root, their relationships and changes along with environmental gradients reflect the adaptation strategies of plant to environmental changes. In this study, three pairs of plant traits, leaf thickness (LT) vs. fine root diameter (RD), specific leaf area (SLA) vs. specific fine root length (SRL), and leaf tissue density (LTD) vs. fine root tissue density (RTD), were selected to analyze the characteristics and relationships of aboveground and belowground traits of dominant and common plant species in different vegetation types along environmental gradients on the northern margin of the Qinghai-Tibet Plateau. Results showed that: (1) The variation of fine root traits was greater than that of leaf traits along with the changes of environmental gradients. From alpine to temperate vegetation, the LT increased, SRL decreased, and other traits had no significant trends. (2) The environmental factors that had the greatest influence on plant traits were the mean annual precipitation (MAP) and growing-degree days above 0℃ (GDD₀). With the increase of MAP, LT and RD showed a decreasing trend in general, SLA first decreased and then increased, and SRL had no significant change. With the increase of GDD₀, LT showed an upward trend, RD first increased and then decreased, SLA generally showed a downward trend, and SRL first decreased and then increased. Among all six traits, LT changed most strongly with the environmental change, while LTD and RTD did not change significantly. (3) In general, there was a significant positive correlation between LT and RD, and a very significant negative correlation between LTD-RTD. With the increase of MAP, the LTD-RTD relationship and SLA-SRL relationship showed the same trends, changing from negative to positive correlations, and LT-RD had no significant correlation in each precipitation slice. With the increase of GDD₀, the relationships of LT-RD and SLA-SRL showed the same trends, i.e., a negative correlation at the low and high GDD₀ end, and a positive correlation at the middle GDD₀ slice. The relationship between LTD-RTD was however not affected by GDD₀. These results revealed that not only plant functional traits change with the environment, but also the plant traits relationships change coping with environmental changes. Such finding is helpful to predict the response and adaption of plant community structure and functions along with changing environments in the context of global change.