【Objective】Biochar is an important soil amendment material, as it plays an increasingly prominent role in carbon sequestration and greenhouse gases mitigations, especially in nitrous oxide (N₂O) mitigation. To investigate the effects and the mechanisms of the biochar aging process on soil N₂O emissions under a rice-wheat rotation system, an in situ field experiment was conducted.【Method】Five treatments were established as follows: CK (without urea and biochar), N (urea), NB_0y(urea with fresh biochar), NB_2y(urea with 2-year aged biochar) and NB_5y(urea with 5-year aged biochar). Soil N₂O emission dynamics were monitored during rice and wheat annual rotation. Also, soil physicochemical characteristics and the abundance of relevant microbial functional genes during the N₂O production process were determined after rice and wheat harvest.【Result】Biochar treatment significantly reduced the cumulative N₂O emissions by 32.4%-54.0%, with the reduction capacity following NB_0y> NB_2y> NB_5y. Compared with the N treatment, NB_0y, NB_2y and NB_5y treatment significantly increased soil pH by 0.6-1.2 units, soil NO₃^--N content by 1.7%-31.3%, and soil organic carbon content by 21.4%-58.6%. Nevertheless, the ability of biochar to improve soil pH was decreased with aging. Also, NB_0y, NB_2y and NB_5y treatments significantly increased the abundance of nosZ gene by 54.9%-249.4%, and the soil (nirS +nirK)/nosZ ratio increased with the biochar age. Meanwhile, the cumulative N₂O emissions showed a significant negative correlation with soil pH, and a positive correlation with NO₃^--N content and amoA -AOB gene abundance.【Conclusion】In summary, both fresh and aged biochar can significantly improve soil physical and chemical properties and decrease soil N₂O emissions, but the effect of fresh biochar was better than that of aged biochar. The mitigation capacity of aged biochar decreased mainly due to the increase of soil NO₃^--N content and (nirS +nirK)/nosZ ratio.