Excessive nitrogen fertilization not only inhibits crop growth but also induces N2O emissions and NH3 volatilization, contributing to environmental pollution. Biochar and biochar-based fertilizers show potential in soil improvement and emission reduction. This study investigated the impacts of different straw-derived biochar application methods combined with chemical fertilizer reduction on N2O emissions and NH3 volatilization in a red soil vegetable greenhouse in Changsha, Hunan Province. Four treatments were established: no fertilization (CK), conventional fertilization (CON), 20% nitrogen reduction + biochar-based fertilizer (BF), and 20% nitrogen reduction + biochar (BC). N2O emissions were monitored via gas chromatography, NH3 was collected using the closed chamber method, and soil nitrogen content and crop yield were measured. Results demonstrated that BF and BC treatments significantly reduced N2O emissions by 27.80% and 12.27%, respectively, with BF exhibiting a 17.70% greater reduction than BC. The N2O emission factor of BF decreased by 33.56% compared to CON, outperforming BC by 33.10%. NH3 volatilization under BF and BC declined by 20.47% and 14.26%, respectively, with BF reducing the NH3 volatilization emission factor by 25.40%, 16.81% lower than BC. BF increased nitrogen use efficiency by 50.91%. Soil NH4+-N decreased by 18.03% and 11.40% under BF and BC, respectively, while NO3--N showed no significant variation. Random forest analysis identified soil NH4+-N, NO3--N, and temperature as key drivers of N2O and NH3 emissions. Fresh weight yields remained consistent across treatments. BF reduced N2O emissions per unit yield by 28.12%. In conclusion, nitrogen reduction combined with biochar or biochar-based fertilizer effectively mitigates N2O emissions and NH3 volatilization in greenhouse vegetable systems, with biochar-based fertilizer demonstrating superior performance.