Large-scale vegetation restoration on the Loess Plateau (LP) has significantly increased regional evapotranspiration (ET), raising concerns about water security. However, the net impact on meteorological drought, which balances moisture supply (ET) and atmospheric demand (PET), has remained poorly quantified. To address this, we employed a counterfactual modelling framework for 2001-2022, using the Standardized Evapotranspiration Deficit Index (SEDI) to compare a "Baseline" (actual greening) scenario against a "Fixed Vegetation" (no greening) scenario. A two-step attribution analysis was then used to quantify the contributions from vegetation structure, CO2 physiology, vegetation physiology, and climate drivers. Results show that vegetation restoration was the primary driver of the 23.2 mm decade-1 ET increase. Despite this, meteorological drought was substantially mitigated: the Baseline SEDI showed a wetting trend of 0.21 decade-1, nearly double the 0.11 decade-1 trend in the Fixed Vegetation scenario. This phenomenon can be explained by two mechanisms: (1) at the component level, vegetation's contribution to ET (17.83 mm decade-1) was almost twice its opposing contribution to PET (9.02 mm decade-1), leading to a net reduction in the atmospheric water deficit; and (2) at the driver level, the wetting trend in SEDI (0.21 decade-1) was mainly driven by favourable climate shifts (0.170 decade-1, 81.4% of the net trend) and reinforced by vegetation structural changes (0.104 decade-1, 49.5%), which together outweighed drying pressures from CO2 physiological (-26.3%) and vegetation physiological (-4.7%) effects. These findings demonstrate that human-led ecological restoration, while increasing total water consumption, has successfully alleviated atmospheric drought. This provides critical scientific evidence for the climate-resilience benefits of the 'Grain for Green' program and offers insights for sustainable water management in other water-limited regions.