Twoseason experiments with three irrigation modes including conventional irrigation (CIR),“thin shallow wetdry” irrigation (TIR) and alternate wetting and drying irrigation (DIR),and two N treatments including 100% ureaN (FM1) and 50% urea N +50% pig manure N (FM2)were conducted.The changes of N2O emission flux,the number of ammonia oxidizing bacteria,potential nitrification rate and inorganic nitrogen content in paddy soil at different growth stages of early rice and late rice were investigated under different irrigation modes and nitrogen (N) treatments to study the effects of ammoniaoxidizing bacteria,potential nitrification rate and inorganic nitrogen content on soil N2Oemission.Results showed that the number of ammonia oxidizing bacteria in paddy soil was lower at the stages of tillering and maturing of early rice and late rice,but higher at the stages of booting and milky.Soil potential nitrification rate was higher at the stages of booting of late rice and the stages of booting and milky of early rice,but lower at the stages of tillering and maturing of early rice and late rice.Under the same N treatment,soil NH4+N content in DIR mode was higher than that in the CIR and TIR modes.Soil NO3-N content in the DIR and TIR modes was significantly higher than that in CIR mode.Soil N2O emission flux at the stages of booting and milky of early rice in the DIR and TIR modes was significantly higher than that in CIR mode.N2O emission flux under FM2 treatment was higher than that under FM1 treatment.The number of ammoniaoxidizing bacteria and potential nitrification rate was significantly positively correlated with soil NH4+N content.Soil N2O emission flux was significantly positively correlated with the number of ammoniaoxidizing bacteria and potential nitrification rate.Paddy soil N2O emission was mainly affected by ammoniaoxidizing bacteria and potential nitrification rate.It is indicated that soil NH4+N content directly affects the number of ammoniaoxidizing bacteria and potential nitrification rate,and affects the N2O emission indirectly.