The Three-North Shelter Forest Program (TNSFP), the largest and most well-established ecological engineering project in the world, is essential for controlling desertification and providing ecological benefits. In this study, we investigate the ecohydrological interactions between surface greening dynamics and groundwater in the Three North Region of China to better understand the sustainability of large-scale restoration strategies. The findings the long-term analysis of groundwater storage (GWSA) and the Normalized Difference Vegetation Index (NDVI) demonstrate that 75.47% of the research region shows non-coherent trends, suggesting an imbalance between surface greening expansion and groundwater accessibility. Conversely, coherent GWSA-NDVI trends were observed in 24.51% of the region, indicating relatively stable hydro-ecological zones in which surface greening and groundwater storage are synchronized. The Granger causality analysis shows that GWSA Granger-causes NDVI in 14.05% of cases and that NDVI Granger-causes GWSA in 47.35% of cases. This imbalance suggests that surface greening may contribute to increased groundwater stress. Finally, afforestation under the TNSFP has changed the surface greening-groundwater interactions in the Three-North China and considerably increased surface greening cover.