In order to explore CO₂ concentration in the sand layer of the mobile sand dunes of the Alxa Desert, and its influence atmospheric CO₂ and its role in the global carbon cycling, the research team utilized infrared CO₂ monitor to observe diurnal variation of CO₂ concentrations in the 19 holes drilled in mobile sand dunes of the desert. Results show that the CO₂ concentration in the air was lower than that in the sands 1 m, 2 m, 3 m, 4 m or 5 m deep, which indicates that the mobile sand dunes with rare plants release CO₂ into the atmosphere both at night and in the daytime during the warm season, acting as CO₂ sources. In the sand layer 5 m deep in the profile, the CO₂ concentration is markedly higher than that in the air, suggesting that the potential of CO₂ release is very big. In the extremely arid part of the Alxa Desert, CO₂ concentration is usually higher in the sand layer 2 m deep than in the layers 1 m, 3 m, 4 m or 5 m deep, but with some individual exceptions. Diurnal variation of CO₂ concentration in the area follows a specific law in all the layers, showing a curve of saddle shape from 08:00 am to 07:00 am the next day, and a significant positive relationship with the temperature in the profile. In that region, the sand layer higher in moisture content is significantly higher in CO₂ concentration, which indicates that moisture content in the sand layers is the major factor determining CO₂ concentration in the layer.