In order to study the effects of atmospheric nitrogen deposition and precipitation changes on herba- ceous plant diversity and above-ground biomass in sand-fixing restoration area of Caragana korshinskii in southern Mu Us Sandy Land，a randomized group design experiment was used to conduct a water and nitrogen addition experi- ment. The experimental scheme was designed in the following way. Four water addition treatments were set： no wa- ter addition (W₀)，33% of average annual precipitation (W₁)，66% of average annual precipitation (W₂)，100% of av- erage annual precipitation (W₃)；Four nitrogen addition treatments were set up，and ammonium sulfate with pure ni- trogen content of 0 g/(m² ·a)(N0)，5 g//(m² ·a)(N5)，10 g/(m² ·a)(N₁₀)，20 g/(m² ·a)(N₂₀) were added respec- tively. and a total of 4 groups were tested for water and nitrogen addition. A combination of one water addition treat- ment and one nitrogen addition treatment which were both randomly selected from the above described four treat- ments to form a combined water and nitrogen treatment for each experiment plot. A total of 16 experiment plots in each block and 4 blocks in total were performed in this study. The results showed as follows：1) Plant community composition and the importance value were significantly affected by water and nitrogen addition (P＜0. 05). Annual and biennial plants were more sensitive to water and nitrogen application than perennial plants，whereas，semishrubs and undershrubs were least affected. 2) Indices of species richness and Shannon-Wiener of the Plant community were significantly affected by water treatment(P＜0. 05)，and both of them increased first and then decreased with water addition，and reached the water threshold at W1 treatment；3) Indices including species richness，Simpson index，and Shannon-Wiener index were all significantly influenced by nitrogen addition(P＜0. 01)，it was found that water addi- tion could compensate the negative effects of increased nitrogen deposition on plant species diversity to some extent， and thus change the composition and structure of plant community；4) Plant community coverage and aboveground biomass were significantly affected by coupling treatments of water and nitrogen (P＜0. 05)；5) The aboveground biomass of the plant community was positively correlated with Shannon-Wiener diversity index，but negatively corre- lated with species richness，Simpson dominance index，and Pielou evenness index. Further more，principal component analysis showed that the W₃-N₁₀ treatment had the best effect on the recovery of herbaceous vegetation productivity in sand -fixing restoration area of Caragana korshinskii，while the W₁ -N₅ treatment had the best effect on restoring the species diversity of herbaceous plant community in this area.