The change in precipitation pattern and increase in atmospheric nitrogen deposition are two important aspects of global change. Both of them closely relate to soil resource availabilities, plant growth, microbial activity, etc., and further posing profound influences on the carbon dynamics in plant-soil systems. Being one of main grassland ecosystem types in northwestern China, desert steppe is limited by soil water and nitrogen availabilities and thus is sensitive to the alterations in precipitation pattern and nitrogen deposition. However, the studies on how the carbon dynamics in desert steppes respond to the two global change aspects are still lacked, especially in those located in Ningxia, northwestern China. To deeply understand the influencing mechanisms of the alterations in precipitation pattern and nitrogen deposition on the ecosystem carbon exchanges in desert steppes, a field experiment was conducted in a desert steppe of Ningxia in 2017. The experiment involved five precipitation treatments (50% reduction, 30% reduction, natural, 30% increase, and 50% increase) and two nitrogen addition treatments (0 and 5 g m^-2 a^-1). The temporal dynamics of net ecosystem carbon exchange (NEE), ecosystem respiration (ER), and gross ecosystem productivity (GEP) were monitored from May to October of 2019. Their relationships with plant community composition and soil properties were analyzed as well. The daily and monthly dynamics of NEE, ER, and GEP increased first and then decreased. NEE was shown as net ecosystem carbon absorption during the whole growing season. Under 0 and 5 g m^-2 a^-1 of nitrogen addition, the decreasing precipitation significantly reduced NEE, ER, and GEP (P<0.05), while 30% increase in precipitation significantly promoted the three indices (P<0.05). Between the same precipitation treatments, nitrogen addition also greatly increased the three indices, especially under the treatment of 50% increase in precipitation. The net ecosystem carbon absorption (represented as-NEE), ER, and GEP were positively related with plant community biomass, Lespedeza potaninii population biomass, and Astragalus melilotoides population biomass. The three indices also enhanced with the increase of Patrick richness index and Shannon-Wiener diversity index. The results above indicate that decreasing precipitation reduces soil water and nutrient availabilities, inhibits plant growth, and thus limiting ecosystem carbon exchange. An appropriate increase in precipitation can promote plant growth and species diversity through increasing soil water content, stimulating soil enzyme activities, regulating soil C:N:P stoichiometric balance, etc., consequently improving the ecosystem carbon sink function. Nitrogen addition also promotes ecosystem carbon exchange. However, its interaction with precipitation is not clear after nearly 3-year experimental treatment. Therefore, a long-term observation is needed for further deeply exploring. The results of this paper will provide data supports for the global networking experiment on ecosystem carbon cycle under global change.