Irrigation regime and fertilizer nitrogen (N) are considered as the most effective agricultural management systems to mitigate greenhouse gas (GHG) emissions from crop fields, but few studies have involved saline-alkaline paddy soil. Gas emitted from saline-alkaline paddy fields (1-year-old and 57-year-old) was collected during rice growing seasons by the closed chamber method. Compared to continuous flooding irrigation, lower average CH 4 flux (by 22.81% and 23.62%), but higher CO 2 flux (by 24.84% and 32.39%) was observed from intermittent irrigation fields. No significant differences of N 2 O flux were detected. Application rates of N fertilizer were as follows: (1) No N (N0); (2) 60 kg ha −1 (N60); (3) 150 kg ha −1 (N150); and (4) 250 kg ha −1 (N250). The cumulative emissions of GHG and N fertilizer additions have positive correlation, and the largest emission was detected at the rate of 250 kg N ha −1 (N250). Global warming potential (GWP, CH 4 + N 2 O + CO 2 ) of the 57-year-old field under the N250 treatment was up to 4549 ± 296 g CO 2 -eq m −2 , approximately 1.5-fold that of N0 (no N application). In summary, the results suggest that intermittent irrigation would be a better regime to weaken the combined GWP of CH 4 and N 2 O, but N fertilizer contributed positively to the GWP.