Dissecting the relationship between plant and soil nitrogen (N) content under climate change is helpful to understand the plant-soil N cycle and reveal the change trend of plant community and soil. This study collected dominant species and soil samples in desert steppe under the six years of factorial experiment of warming (ambient temperature, warming 2℃ and warming 4℃) and increasing precipitation (natural precipitation, increasing precipitation by 25% and 50%). By measuring and analyzing the total nitrogen (TN), available nitrogen (AN) and stable nitrogen isotopes (δ¹⁵N) of leaves and soils, we explored the change trend of N content of plants and soil in desert steppe after warming and increasing precipitation, and revealed the main factors controlling the plant-soil N cycle. The results show that:(1) warming and the interaction of warming and increasing precipitation insignificantly increased the TN, AN and δ¹⁵N of soil (P>0.05). Increasing precipitation significantly reduced the AN of soil (P<0.05). (2) Warming activated nitrogen competition among species, which increased the leaves TN of Stipa breviflora and Neopallasia pectinata and decreased the leaves TN of Artemisia frigida and Allium mongolicum. Increasing precipitation and the interaction of warming and increasing precipitation significantly reduced the leaves TN of four species, which may be regulated by soil AN. (3) Warming enriched the δ¹⁵N of leaves, and increasing precipitation depleted the δ¹⁵N of leaves. The δ¹⁵N of leaves was regulated by temperature, precipitation, the δ¹⁵N of soil and the TN of leaves. Therefore, warming stimulated the N competition among species in desert steppe, which contributed to the absorption and accumulation of N by Stipa breviflora and Neopallasia pectinata, which may increase their proportion in plant communities. In addition, precipitation plays a leading role in the plant-soil N cycle of desert steppe and frequent precipitation events may exacerbate nitrogen limitation in desert steppe.