[Objective] Nitrous oxide (N₂O) and nitrogen (N₂) are important gaseous products of denitrification in soil profile of flooded rice field, which may be discharged directly into the atmosphere through soil-water interface, or leached into groundwater and eventually into the atmosphere. Application of biochar can alter denitrification process in the paddy field by changing physicochemical and microbiological properties of the paddy soil and then affect the generation and emission of N₂ and N₂O in the field.[Method] In this study, based on a long-term (since 2010) rice-wheat rotation field experiment on biochar amendment. Soil solutions (0-1 m depth) were collected through specially designed piezometers imbedded in the paddy soil. And concentrations of dissolved N₂O and exN₂(N₂ produced by denitrification) in soil solution were determined by gas chromatography and membrane inlet mass spectronmeter. The experiment was designed to have 4 treatments (CK:each season 0 t·hm^-2; 1BC:each season 2.25 t·hm^-2; 5BC:each season 11.3 t·hm^-2; 10BC:each season 22.5 t·hm^-2) for the two rice seasons in 2018 and 2019, and aimed to investigate spatial and temporal variations of N₂O and exN₂ concentrations in soil solution as affected by biochar application rate. The effects of long-term application of biochar on denitrification in paddy soil profile and the exN₂, which was the main gaseous nitrogen product, was washed away by water were evaluated.[Result] The concentration of N₂O is higher in the soil 60 cm in depth in CK and exN₂ concentration decreased with soil depth. N₂O and exN₂ concentrations in profile decreased with rising biochar application rate, thus being the lowest in treatment 10BC. Among them N₂O concentration decreased the most significantly in the soil 60 cm in depth and exN₂concentration decreased with increasing soil depth. Biochar amendments had no obvious effect on inorganic nitrogen (NO₃^- +NH₄⁺) in the soil profile, but increased the concentrations of soluble organic carbon (DOC), dissolved oxygen(DO) and redox potential (Eh) in 5BC and 10BC. The variations of N₂O and exN₂ was related to DOC, NO₃^- and DO in CK, and to DO and Eh in the biochar treatments. The leaching amount of exN₂(calculated by 1 m depth) is 2.3-5.5 kg·hm^-2 in CK, which was equivalent to 32%~34% of the leaching amount of inorganic nitrogen and organic nitrogen (DON), while it was reduced to 1.7-3.7 kg·hm^-2 and 1.1-1.9 kg·hm^-2 in 5BC and 10BC.[Conclusion] All the findings show that the leaching amount of N₂ produced by denitrification with water can not be ignored, the amendment of biochar can improve aeration of the soil profile and increase DO and Eh, thus inhibiting denitrification and reducing the risk of leaching loss of its main gaseous products, exN₂.