In order to explore the effect of water and nitrogen coupling on CH4 emission in black soil paddy fields with straw returned to field, explore the water and fertilizer management mode of saving water and reduce emissions, and achieve the goal of yield increassing, on the basis of straw returning to the field, two irrigation modes of conventional flooding irrigation and controlled irrigation were set up, and four nitrogen fertilizer gradients were set up. The CH4 emission fluxes of each treatment were observed by static box gas chromatography, the water and nitrogen were analyzed. Under the coupling, the redox potential of paddy soil, the content of soil ammonium nitrogen and nitrate nitrogen in each growth stage, the change of straw decomposition rate, and the influence of each factor on CH4 emission in paddy field were calculated. The results showed that the CH4 emission flux and cumulative emission of conventional flooding irrigation were significantly higher than that of control irrigation （P<0.05), and the CH4 emission flux and cumulative emission were increased significantly with the increase of nitrogen application level （P<0.05);compared with normal irrigation, the cumulative emission of CH4 was increased by 16.24% （P<0.05) and the yield was decreased by 2.01% on average with the increase of nitrogen application. Under conventional flooding irrigation, the application of nitrogen fertilizer had little effect on the yield, but also reduced the cumulative emission of CH4 by 18.59%（P<0.05);if the application of nitrogen reduction was under controlled irrigation, the cumulative emission of CH4 was decreased by 62.71%（P<0.01), and the yield was increased by 21.16%（P<0.05). Through the correlation analysis, it was found that the amount of nitrogen application, irrigation method and their interaction had a significant impact on CH4 emissions;under the coupling of water and nitrogen, the content of ammonium nitrogen in paddy soil, the decomposition rate of straw and CH4 emissions had a significant positive correlation（P<0.05),and the redox potential of soil had a significant negative correlation with CH4 emissions（P<0.05). In consideration of comprehensive emission reduction benefits, the economic benefits can be maximized by using controlled irrigation and appropriate nitrogen fertilizer reduction under straw returning, so as to achieve the purpose of water saving,emission reduction and production increase.