In order to clarify the effect of soil moisture content on the growth and nitrogen uptake preference of ephemeral plants in desert ecosystems, we selected four dominant ephemeral plants in the Gurbantunggut Desert, Eremopyrum orientale, Erodium oxyrhinchum, Centaurea pulchella, and Lappula patula as the research object. Through the potted water control experiment, setting 3 water gradients: drought treatment (W₁, soil water content 2%)， normal moisture treatment (W₂, soil water content 8%), wet treatment (W₃， soil water content 14%). Using the ¹⁵N isotope tracer method, we studied the effects of water on biomass and nitrogen uptake strategies of four plant species. The results showed: (1) with the increase of the soil moisture content, the aboveground, underground and total biomass of the four ephemeral plants showed an increasing trend, and the growth rate is the highest under normal water treatment, and the biomass accumulation rate was different among different species in the same lifeform. However, the rootshoot ratio of four ephemeral plants decreased significantly with the change of soil moisture content. (2) Under different water treatments, the ¹⁵N uptake rates of the four ephemeral plants for different forms were as follows: nitrate nitrogen > ammonium nitrogen > glycine, and the uptake rates of the three forms of nitrogen and total nitrogen increased with the increase of the water gradient. (3) In drought treatment, nitrate nitrogen was the most preferred nitrogen form to be absorbed by the four ephemeral plants. With the increase of soil moisture content, the nitrogen form preference of Eremopyrum orientale and Centaurea pulchella were not changed. However, when the water continued to increase to wet treatment, the contribution rate of ammonium nitrogen to the nitrogen uptake of Erodium oxyrhinchum and Lappula patula exceeded the nitrate nitrogen, became the most preferred form of nitrogen absorbed by these two plants.