Abstract: The effect of Na⁺ on the photosynthetic characteristics of seedlings of the succulent xerophyte Zygophyllum xanthoxylum were investigated under -0.5 MPa osmotic stress. Under this stress, the leaf area, chlorophyll (a+b) content, net photosynthetic rate (Pn), stomatal conductance (Gs) and phosphoenolpyruvate carboxylase (PEPCase) activity were significantly elevated by 105%, 33%, 115%, 90%, and 180% respectively at 50 mmol/L NaCl, but the intercellular CO₂ concentration (Ci) was significantly reduced by 17%. In addition, the potential photosynthetic activity (F_v/F₀), primary light energy conversion efficiency (F_v/F_m), and photosynthetic electron transport rate (ETR) of PSⅡ were enhanced by 15%, 5%, and 11% respectively. These results indicate that, under -0.5 MPa osmotic stress, Na⁺ can improve the photosynthesis of Z. xanthoxylum seedlings and enhance the osmotic stress resistance of plants.