Using desert C₃ plant Reaumuria soongarica and C₄ plant Salsola passerina as materials, along the natural precipitation gradient in the arid desert region of Northwest China, the solitary and mixed R. soongarica and S. passerina roots, stems and leaf organs under different precipitation conditions we measured carbon, nitrogen, and phosphorus stoichiometry indicators, and analyzed their stoichiometric characteristics in different habitats in response to interspecific relationships and environmental stress. The results showed that: (1) with the increase of drought stress (decrease in precipitation), the C content of various organs of R. soongarica increased by 7.73% on average, and the N and P contents decreased by 6.20% and 10.61%, respectively; the C content of S. passerina increased by 7.36% on average, and the N and P contents decreased by 5.93% and 14.03%, respectively. The increased C content in the leaves of the two plants indicates that their photosynthetic rate is low and their growth is slow. However, they have a strong defense ability against the adverse external environment and can better adapt to the drought environment. (2) Drought stress changed the distribution patterns of C, N and P in different organs of R.soongarica and S. passerina, and the N content and N/P ratio were higher in leaves than that in roots. The N/P of R. soongarica and S. passerina was significantly higher in roots and leaves than that of stems, indicating different nutrient limitation in different organs of the two plants. (3) The contents of C, N and P in R. soongarica are higher than that in S. passerina, which indicates that R. soongarica has strong defensive ability, fast growth rate and strong ability to compete and utilize resources. C/N and C/P of S. passerina were higher than those of R. soongarica, indicating that S. passerina had stronger carbon assimilation ability and higher nutrient use efficiency. (4) Under drought stress condition, both R. soongarica and S. passerina showed a pattern of carbon accumulation and nitrogen and phosphorus limitation. They were inactive in nitrogen and phosphorus nutrient utilization, and were more balanced by the nitrogen and phosphorus limitation.