Excessive application of nitrogen fertilizers in facilitated vegetable fields may easily lead to soil degradation (such as soil salinization，acidification，hardening, etc.), and even further to some serious environmental consequences like pollution of groundwater and emission of large volumes of N₂O, thus seriously affecting sustainable development of the vegetable industry. Recently, a novel soil remediation technology, called RSD(reductive soil disinfestation) has been developed of adding organic substances (e.g., crop straw, molasses, manure, etc.) in flooding water. The RSD method can effectively alleviate the risk of soil degradation, such as removing the nitrate accumulated in the soil, increasing pH, lowering soil electrical conductivity and improving soil structure. However, in strong reducing environments the high amount of nitrate accumulated in the degraded facilitated vegetable fields was rapidly reduced by denitrification, and high nitrous oxide (N₂O) emission was observed in RSD process. N₂O is the third major greenhouse gas, and is 296~310 times as high as CO₂ in global warming potential. It is estimated that N₂O emitted from agricultural soil accounts for 60% of the annual anthropogenic emission into the atmosphere, and the facilitated vegetable soil with high N input is one of the most important agricultural N₂O sources, contributing about 20% to the emission from agricultural soil. Therefore, it is essential to investigate how to mitigate N₂O emission from degraded facilitated vegetable soil, especially in its strong reductive remediation process. In this study, Biochar was selected as soil regulator in evaluating effects of the use of biochar on N₂O emission in degraded vegetable soil and its RSD process relative to rate of its use. Six treatments were designed and conducted, Treatment CK (16% in soil moisture content and no biochar used), Treatment 1% BC(16% in soil moisture content and 1% biochar applied, w/w), Treatment 5% BC (16% in soil moisture content and 5% biochar applied), Treatment RSD (flooded, rice straw incorporated and no biochar used), Treatment RSD + 1% BC (RSD and 1% biochar applied) and Treatment RSD + 5% BC (RSD and 5% biochar applied). By determining the abundance of nitrifying functional genes (norB gene andnosZ gene encoding nitric oxide reductase and nitrous oxide reductase, respectively), activities of denitrifying microorganisms were characterized. Soil samples were collected from the treatments and incubated at 30 ºC in dark for 14 days,and N₂O emission rate was measured during the incubation using the accumulative method. Besides, soil samples were also collected for analysis of inorganic nitrogen contents, soil pH and abundance of denitrifying functional genes. Each sampling had four replicates. Results show that RSD significantly lowered soil nitrate content, raising soil pH and retarded soil degradation, but the cumulative N₂O emission from the RSD-treated soils was over 950 times as high as that from their non-RSD treated counterparts. Application of 5% Biochar reduced the N₂O emission in degraded vegetable soil and its RSD process by 68.7% and 16.0%, respectively. Pearson correlation analysis reveals a negative relationship between N₂O emission rate and soil pH in both degraded vegetable soil and its RSD process, and a positive relationship between N₂O emission rate and soil ammonium content in RSD process. The abundance of norB and nosZ genes was also significantly changed after biochar application. Linear regression analysis shows that soil N₂O emission was mainly related to nosZ gene abundance in degraded vegetable soil, but to norB gene abundance in RSD process. To sum up, the application of 5% biochar in degraded vegetable soil and its RSD process can elevate soil pH and alter abundances of the critical denitrifying functional genes, thus efficiently mitigating N₂O emission. All the findings in this study may serve as experimental evidence for N₂O mitigation in degraded vegetable soil, and also can be regarded as important indices for assessment of environmental effects of the remediation of degraded vegetable soil.