Abstract: The atmospheric CO₂ concentration has an obvious rising trend with the increasing global climate change, which will indirectly affect the nitrogen cycling process of the soil-plant-microbe system. In order to investigate the mechanisms of the rising CO₂ effect on denitrifying bacteria in paddy soil, we used the airtight rice incubator and the real-time PCR technology to investigate the effect of the elevating CO₂ concentration on the abundance of narG-, nirK-and nirS-containing bacterial communities at two nitrogen levels. The results showed that the elevating CO₂ concentration significantly increased the biomass of roots and aboveground parts (2.96%-28.4%, 7.1%-107.3%) at the tillering, booting, blooming and maturing stages either without nitrogen or with regular nitrogen application. Meantime, the dry weight of grains at the two levels of nitrogen application increased (19.5%, 38.0%) at the maturing stage, indicating that the rice yield was stimulated by the elevating CO₂ concentration; Response of denitrifying bacteria to elevating CO₂ concentration was related to growth stage and nitrogen application level:the elevating CO₂ decreased the number of denitrifying bacteria at tillering stage, but increased that at booting stage; The elevating CO₂ obviously increased the abundance of narG-, nirS-containing communities in nitrogen application treatment at the booting stage, and decreased the abundance of narG-, nirK-and nirS-containing communities at the maturing stage. In addition, the abundance of narG-, nirK-and nirS-containing communities were narG > nirS > nirK, and they decreased with the increase of rice growth. Both nirK and nirS genes belong to nitrite reductase, but the abundance of nirS gene was higher than that of nirK, and their responses to elevating CO₂ and nitrogen application were different. Overall, the results showed that the elevating CO₂ significantly increased rice growth and yield, and the effects of CO₂ on the abundance of denitrifying bacteria in paddy soil were different with different nitrogen application.