Populus pruinosaSchrenk has the biological characteristics of heteromorphic leaves and is a pioneer species for wind prevention and sand fixation. The functions of heteromorphic leaves at different developmental stages and canopy heights ofP. pruinosaare unclear. To clarify how developmental stages and canopy height affect the functional characteristics of leaves, this study evaluated the morphological anatomical structures and the physiological indicators of leaves at 2, 4, 6, 8, 10, and 12 m. The relationships of functional traits to the developmental stages and canopy heights of leaves were also analyzed. The results showed that blade length (BL), blade width (BW), leaf area (LA), leaf dry weight (LDW), leaf thickness (LT), palisade tissue thickness (PT), net photosynthetic rate (Pn), stomatal conductance (Gs), proline (Pro), and malondialdehyde (MDA) content increased with progressing developmental stages. BL, BW, LA, leaf dry weight, LT, PT, Pn, Gs, Pro, and the contents of MDA, indoleacetic acid, and zeatin riboside had significant positive correlations with canopy heights of leaves and their developmental stages. The morphological structures and physiological characteristics ofP. pruinosaleaves showed more evident xeric structural characteristics and higher photosynthetic capacity with increasing canopy height and progressive developmental stages. Resource utilization efficiency and the defense ability against environmental stresses were improved through mutual regulation of each functional trait.