【Objective】Nitrous oxide (N₂O) is an important greenhouse gas, which is 298 times higher than carbon dioxide in Global Warming Potential (GWP) over a time scale of one hundred years.With the widespread application of chemical fertilizers and the practice of water management of alternation of drying and wetting, paddy soil has become an important source of nitrous oxide emissions.Researches show that the process of flooding-draining paddy fields can cause emissions of large amounts of nitrous oxide, and variation of the redox potential during the process is closely related to N₂O emission. Iron is a crucial redox element in paddy soil, but its influence on N₂O emission is not clear. The study is oriented to expose impacts of Fe on N₂O emission and denitrifying microorganisms. 【Method】An in-lab soil incubation experiment was carried out using samples of the paddy soil derived from the quaternary red clay. The experiment was designed to have three levels of ferrihydrite amendment (Fe 0, 10 and 40 μmol g^-1 soil) and two levels of soil water content (50% and 80%). The soil samples were air-dried and sifted through a 1mm sieve. According to the designing of the experiment, the pretreated soil samples were fully blended with ferrihydrite, separately, put into 1-L plastic boxes, 200 g soil on a dry weight basis in each box, and then spiked with KNO₃solution to ensure the samples 1.6 μmol g^-1 soil in N content and 50% or 80% in soil water content, separately. The boxes of soil samples were placed into an incubator, 28℃in temperature and kept there for 24h.Air and the soils in the boxes were sampled once every 6 h during the incubation for analysis N₂O concentration in the air sample was determined with a Gas-chromatograph. Soil samples for physical and chemical analysis were stored at 4℃ and analyzed for NH₄+-N and NO₃--N contents with a continuous flow analyzer, while soil samples for microorganism analysis were quick-frozen in liquid nitrogen, and stored at -80℃, and then analyzed for variations of the communities and populations of soil denitrifying microorganisms with a realtime flourescentquantification polymerase chain reaction (qPCR) and a terminal-restricted fragment length polymorphism (T-RFLP). 【Result】Results show that during the process of N₂O emission rate rising to a peak, denitrification was obviously disturbed. In the treatments spiked with extraneous iron, especially at high rates (40 μmol g^-1), nitrate concentrations were much higher than in CK, while N₂O emission rates were significantly lower than in control. However, after the peak, N₂O emission rate decreased markedly in all the treatments, but it did much more slowly in the treatments spiked with high rates of iron than in CK and consequently remained higher than that in CK. Meanwhile, during the first 12 hours of incubation, the abundance of nitrate reductase gene (narG) and nitrous oxide reductase gene (；nosZ) varied significantly, demonstrating that the ferrihydrite spiked apparently inhibited the growth of narG- and ；nosZ-containing communities in population size, and the more ferrihydrite was added and the more obvious was the effect. However, after 12 hours, the inhibition effect was no longer so obvious. The addition of extraneous iron did not have much influence on structure of the denitrifying microorganism community. 【Conclusion】So it is concluded that the effect of Fe (Ⅲ) affecting population of the denitrifying microorganism community is the main cause of extraneous Fe (Ⅲ) inhibiting N₂O emission during the early period of the incubation, and hence nitrate reduction and N₂O production. But in the late period of the incubation, the recovery of denitrifying microorganisms in abundance and the existence of nitrate-containing residues, like NO₃-,pushes the N₂O emission rate higher in the treatments spiked with extraneous iron than in CK.