Understanding the mechanisms driving terrestrial carbon sequestration is essential for guiding ecological restoration and climate mitigation strategies. The Yellow River Basin (YRB), a key ecological zone in northern China, has experienced significant vegetation structural changes since 2000, characterized by widespread greening and increased leaf area index (LAI). However, the relative contributions of vegetation dynamics and environmental drivers to carbon sequestration remain insufficiently quantified. In this study, we employed a model-data fusion approach by integrating the remote sensing-driven ecosystem process model (CEVSA-ES) with multiple observational datasets to quantify the spatiotemporal dynamics and driving forces of carbon sequestration in the YRB from 2000 to 2022. Validation against observational data confirmed that CEVSA-ES effectively captured the interannual variability of major carbon fluxes. The multi-year average annual carbon sequestration was 24.79 +/- 10.61 Tg C a(-1) in the YRB during 2000-2022. Over the same period, the carbon sink increased significantly (p < 0.001) at an average rate of 1.38 Tg C a(-1). LAI-driven canopy dynamics emerged as the dominant contributor, accounting for 54.35 % of the total increase, primarily through vegetation growth in areas without land use change (46.38 %). Land use/cover change (LUCC) contributed an additional 7.98 %, largely driven by afforestation. The CO2 fertilization effect explained 29.71 % of the increase, while climate change and nitrogen deposition contributed 6.52 % and 0.72 %, respectively. Spatially, vegetation greening was the key driver in the upper and middle reaches, while CO2 fertilization dominated in the source region. These findings highlight the pivotal role of vegetation structure optimization-beyond LUCC-in enhancing carbon sink capacity in semi-arid regions. The results underscore the importance of integrating vegetation dynamics into land management policies and support the implementation of nature-based solutions for carbon neutrality and sustainable watershed development.