The effect of elevated atmospheric CO_2 concentrations was investigated on soil fauna communities, controlling the concentrations at 370, 550 and 700 ppm in open top chambers in Sanjiang Plain. Samples were taken and separated by Tullgren or Baermann funnel methods in autumn 2017. Our results showed that: (1) 6,268 individuals belonging to seven classes and 15 orders were collected. Oribatida was the dominant group, accounting for 88.13% of the total individuals. Collembola and Diptera larvae were the other most common groups, accounting for 9% in total, respectively. Different groups varied in their responses to elevated CO_2 concentrations. Oribatida was the dominant group. Collembola and Diptera larvae were the most common groups in AC, EC1 and EC2, but rare groups also differed in AC, EC1 and EC2. (2) The elevated CO_2 concentration significantly increased the density of Oribatida, but reduced the density of Collembola. However, no other soil fauna were significantly affected. (3) The Shannon-Wiener index and the Pielou index of soil fauna exhibited the order of AC > EC1 > EC2, the Simpson index showed the order of EC2 > EC1 > AC, and the Margalef index showed the order of AC > EC2 > EC1. Our results indicate that the soil fauna community composition and diversity might be affected by climate change.