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A field experiment was conducted to explore the effects of different water and nitrogen coupling methods on the carbon balance of paddy ecosystem in 2022. Two irrigation modes (conventional flooding irrigation (F) and rice-controlled irrigation (C)) and three nitrogen application levels (conventional nitrogen application-level (N, 110kg/hm2), 10% nitrogen reduction-level (N1, 99kg/hm2) and 20% nitrogen reduction-level (N2, 88kg/hm2)) were set up in the experiment. The effects of different water and nitrogen coupling on dry matter weight, carbon content, soil respiration CO2 emission flux, CH4 emission flux, and total emissions of both were analyzed. The net ecosystem carbon budget (NECB) evaluation system was used to analyze the carbon source and sink effect of ecosystem in black soil paddy fields. The results showed that under different water and nitrogen coupling modes, the carbon sequestration of rice panicles and roots accounted for 26.61%~40.92% and 24.63%~31.95% of the total carbon sequestration, respectively. Under the same nitrogen application rate, C can improve the carbon content and dry matter weight of rice organs compared with F. During the whole growth period of rice, the CH4emission flux of each treatment showed a trend of increasing first, then decreasing before increasing, and peaked at tillering stage and jointing-booting stage. The soil respiration CO2 emission flux of each treatment showed a single peak variation, and the peak appeared at the tillering stage. Under the same irrigation mode, except for the regreening period, the CH4 emission flux and soil respiration CO2 emission flux of each treatment was decreased with the decrease of nitrogen application rate. Under the same nitrogen application rate, compared with rice control irrigation, F reduced soil respiration CO2 emission flux and total emission, but increased CH4 emission flux and total emission. Under different water and nitrogen coupling modes, the net primary productivity of rice was 4245.82~6958.19kg/m2, the net primary productivity of panicle was the highest, and the net primary productivity of litter was the lowest, accounting for 42.88%~51.82% and 3.19%~3.90% in the net primary productivity of rice, respectively. Under the same nitrogen application rate, the net primary productivity of rice in each treatment of C mode was higher than that of conventional irrigation mode. Compared with FN, FN1 and FN2 treatments, the net primary productivity of CN, CN1 and CN2 treatments was increased by 11.17%, 31.92% and 2.98%, respectively. In addition, the NECB of different water and nitrogen coupling modes was positive, which indicated that the paddy ecosystem in the black soil area was a net carbon “sink”. The net carbon budget of CN1 treatment (1082.87kg/hm2) was significantly higher than that of other treatments (P<0.05), which indicated that the carbon “sink” intensity of paddy ecosystem with 10% nitrogen reduction under controlled irrigation mode was the largest.