<p>Vegetation plays a dual role in enhancing carbon sequestration while influencing ozone (O₃) formation through biogenic volatile organic compounds (BVOCs). Yet, the relative contributions of these processes and their spatial coupling remain poorly quantified, limiting our understanding of the co-benefits and trade-offs between air quality improvement and carbon mitigation. In this study, we established an integrated modeling framework that couples land-use, vegetation dynamics, and atmospheric chemistry to quantify the co-effects of vegetation on air quality and carbon sequestration. The results show that vegetation dynamics enhanced China’s terrestrial carbon sink by 73.7–151.9 Tg C yr^–1 and increased BVOC emissions by 13.6–17.5 Tg, leading to 9.1–10.5 μg m^–3 increases in surface O₃ concentrations. Both O₃ and carbon sinks exhibited pronounced spatial heterogeneity. Regions where enhanced carbon sinks coincided with elevated O₃ were mainly located in Northeast China, the North China Plain, and Central China. In contrast, co-beneficial regions, characterized by simultaneous increases in carbon sinks and decreases in O₃, were concentrated in southeastern China. These findings provide the first spatially explicit evidence of heterogeneous trade-offs and synergies between air-quality improvement and carbon sequestration, offering scientific guidance for coordinated land-use planning and vegetation management under future climate scenarios.</p>