【Objective】The objective of this paper was to explore the impacts of one-off fertilization on CH_4 and N_2O emissions and its impacting factors in rape-paddy replanting system to calculate global warming potential,and to understand the contribution of one-off fertilization to the greenhouse gas emission,so as to provide scientific basis and technical reference for greenhouse gas emission reduction.【Method】Based on the typical rape-paddy replanting system in the middle and lower reaches of the Yangtze River,the experiments were set up in the (30.36N,112.08E) rape-paddy replanting test field in Taihu port farm of Jingzhou from October 2015 to September 2016 with 5 treatments,including Control treatment (CK),Farmers' Practice treatment (FP),Optimal fertilizer treatment (OPT),Urea fertilizer treatment (UA) and Controlled release fertilizer treatment (CRF),with 3 replicates.In the whole growth period,the static chamber gas chromatography method was used for determination of CH_4 and N_2O emission flux.Before and after planting,the physicochemical properties of soil and yield of the crop were measured.【Result】(1) The emissions of N_2O and CH_4 had obvious seasonal dynamics of high in paddy season and low in rape season.The fluxes of N_2O varied -4.08-35.51 mug N·m~(-2)·h~(-1) and varied -16.52-193.30 mug N·m~(-2)·h~(-1) in the paddy season.The average annual emission flux varied 3.66-23.70 mug N·m~(-2)·h~(-1);the fluxes of CH_4 varied -0.08-0.05 mg C·m~(-2)·h~(-1) in rape season.The fluxes of CH_4 in rice season varied -0.54-4.81 mg C·m~(-2)·h~(-1).The annual average flux varied 0.42-0.66 mg C·m~(-2)·h~(-1).(2) The amounts of N_2O emissions from high to low were FP,CRF,OPT,UA,and CK,respectively,and the value of them was 1.31,1.19,1.04,0.82 and 0.37 kg N·hm~(-2),respectively.The emission factors were a range in 0.14%-0.25%,all values were lower than 1%,which were IPCC Recommended.Compared with OPT treatment with the same amount of nitrogen input,the two one-off fertilization UA and CRF treatments could effectively reduce CH_4 emissions by 29.0% and 29.9%,respectively,at the same time UA treatment can reduce the 21.2% N_2O emissions,but CRF treatment increased 14.8% N_2O emissions.(3) Under the same amount of nitrogen application,one-off fertilization CRF significantly increased the yield of rape by 10.6%,while the effect on paddy yield was not significant.The characteristics of the GHGI showed low in rape season,high in rice season,but there was no significant difference in treatments between rape and rice season.The minimum GHGI of CRF and UA in rape season was 0.038 kgCO_(2-eq)·kg~(-1),OPT was maximum with 0.057 kgCO_(2-eq)·kg~(-1),the minimum of UA in rice season UA was 0.07 kgCO_(2-eq)·kg~(-1),and FP was maximum with 0.13 kgCO_(2-eq)·kg~(-1).(4) The Global Warming Potential of the two gases were integrated with the GWP (100 year scale),under the same nitrogen application amount,one-off fertilization UA and CRF were better than OPT significantly reduced the GWP 28.0% and 18.2% (P<0.05),and the one-off fertilization of urea was more effectively reduce the effect of greenhouse gas.【Conclusion】For the typical farmland in the middle and lower reaches of the Yangtze River,one-off fertilization of common urea or control-release urea could reduce greenhouse gas emissions while maintained crop yield,but it still needs to be verified by long-term experiments.