Observation was performed during the period from April, 2015 to August, 2015 of N2O emissions from long-term irrigation field under different irrigation managements: Drip irrigation (D30), subsurface irrigation (S30) and furrow irrigation (G30) during the tomato season, using the static chamber-gas chromatograph method and Real-time quantitative polymerase chain reaction (Real-time PCR) technique. In order to find the relationship between the N2O emissions and impact factors, soil temperature, soil moisture, soil mineral nitrogen and soil denitrifying bacteria were observed in the meanwhile, which conducted by the combination of field experiments and laboratory analysis. Results showed that N2O emission peaks would obviously occur within 1～8 days after each irrigation. In tomato growth season, soil N2O mean fluxes was highest under furrow irrigation treatment, 52.74% higher than drip irrigation treatment and 50.82% higher than subsurface irrigation treatment; compared with furrow irrigation, the soil N2O total fluxes significantly decreased by 54.31% and 53.30%. Soil N2O emissions were very significant positive correlation with soil moisture (P＜0.01) and nitrate nitrogen concentration (P＜0.05). There was no consistent correlation between soil N2O fluxes and soil temperature, soil ammonium nitrogen content. Abundances of soil denitrifying bacteria had significant difference under different irrigation managements, followed by G30＞S30＞D30. Abundances of soil denitrifying bacteria nosZ were related to the soil N2O emissions (P＜0.01). In conclusion, soil moisture, nitrate nitrogen, denitrifying bacteria nosZ were important factors that affected the soil N2O emissions; choosing drip irrigation and subsurface irrigation could effectively reduce N2O emissions from the greenhouse soil.