A 6-year biochar and straw return experiment with a winter wheat-summer maize rotation system in the North China Plain investigated the effects of biochar and straw return on CO₂ and N₂O fluxes using the static chamber/gas chromatography method. The experiment consisted of four treatments with three replicates. The treatments were CK (control), C1 (biochar 4.5 t hm^-2 a^-1), C2 (biochar 9.0 t hm^-2 a^-1), and SR (straw return). The results showed that the CO₂ and N₂O fluxes trends were generally the same throughout the whole rotation period. After applying the biochar, the CO₂ fluxes increased 0.3%-90.3% (C1), 1.0%-334.2% (C2), and 0.4%-156.3% (SR). The C2 treatment had the greatest effect on CO₂ cumulative emissions, with an increase of 42.9%. The N₂O flux results showed that the C2 treatment significantly (P < 0.05) reduced cumulative N₂O emissions, but increased the comprehensive warming potential of CO₂ and N₂O emissions. In contrast, the C1 and SR treatments had no significant effect on cumulative N₂O emissions and the comprehensive warming potential. The correlation analysis showed that CO₂ flux was significantly positively (P < 0.01) correlated with soil temperature and soil water content, and that the N₂O flux was significantly positively (P < 0.01) correlated with soil temperature, soil water content, NO^- ₃-N, and NH₄⁺-N, but significantly negatively (P < 0.01) correlated with soil pH. In summary, the addition of biochar has the potential to significantly reduce nitrogen gas loss.