Leaf vein plays an important role in maintaining leaf water state and photosynthetic capacity. Knowledge of the variation in leaf vein traits along the environmental gradient is helpful for us to explore the plants' adaptive strategies to environmental changes from the perspective of plant physiological structure. In this study, we selected 10 sampling sites from east to west along the water and nutrient gradients in the middle of the Loess Plateau, which covered the three vegetation types, including forest grassland, typical grassland and desert grassland. In total, the leaves of 519 plant species were sampled and their leaf vein traits were measured, including vein length per leaf area (VLA, mm/mm²), vein diameter (VD, μm), and vein volume per leaf area (VV, μm³/mm²). We aimed to explore the relationships among three leaf vein traits of different leaf vein types (i.e., reticulate vein, parallel vein and single vein) and their variation along environmental gradients. The results showed as follows:(1) In Loess Plateau, the VD and VV increased with the decrease of longitude, while VLA did not change significantly along the longitude (P>0.05). (2) In plants of different leaf vein types, the negative correlation between VLA and VD was only found in reticulate vein and parallel vein, the positive correlation between VLA and VV was only found in reticulate vein. However, the positive correlation between VD and VV was found in all leaf vein types. (3) As the longitude decreased from east to west, three leaf vein traits of reticulate vein plants significantly increased (P<0.01), but these variation trends were all weak (R²=0.02-0.07). For parallel vein plants, VLA did not exhibit significantly trend along the longitude (P>0.05), while VD and VV decreased significantly as the longitude decreased (P<0.01). However, there were no significantly longitudinal patterns in the three leaf vein traits of single vein plants (P>0.05). (4) Vein type was the main factor driving the variation of leaf vein traits, with 27.84%-62.25% of the total variation explained. Among the environmental factors, the influences of soil factors, especially soil moisture and nutrient content, on the three leaf vein traits were greater than those of climate factors (0.54%-2.91% vs. 0.02%-0.77%). The results indicated that different leaf vein-type plants usually had different adaptive strategies. Therefore, the effect of leaf vein types should be taken into consideration when studying the response and variation of leaf vein to environmental changes in the future.