Abstract: Two dominant ephemeral plants, i.e., Erodium oxyrhinchum M. Bieb. and Eremopyrum orientale (L.) Jaubert & Spach, from the Gurbantünggüt Desert were used for potted plant experiments under controlled conditions. We set two temperature gradients and three moisture gradients to analyze variation characteristics in carbon (C), nitrogen (N), and phosphorus (P) contents and their stoichiometric ratios under different temperature and humidity treatments. Results show that: (1) Temperature significantly affected N, P contents, C∶P, and N∶P in Erodium oxyrhinchum, and C, N, P, C∶N, and N∶P in Eremopyrum orientale. Water significantly affected N, P, C∶N, and C∶P in both plants and N∶P in Eremopyrum orientale. The changes in N content with temperature conformed to the temperature-biogeochemical hypothesis, while the changes in P content with temperature conformed to the temperature-plant physiology hypothesis. (2) Interactions between temperature and water also affected the plants. Under high temperature treatment, as the water gradient increased, N and P contents in both plants first increased and then decreased, while C∶N, C∶P, and N∶P first decreased and then increased. Under low temperature treatment, changes in N and P contents in Erodium oxyrhinchum were inversely proportional to the water gradient, while changes in C∶P were directly proportional to the water gradient. However, the stoichiometric changes in Eremopyrum orientale were not significant. (3) Correlation analysis showed that temperature and water significantly affected element correlations in both plants, and the growth rates and nutrient limitations of the plants were also subject to dominant regulation of the nutrient elements.