<p>Large-scale ecological restoration programs have been widely implemented to alleviate ecological degradation and environmental stress in arid and semi-arid regions. However, evaluating their long-term ecological effectiveness remains challenging, particularly across large spatial extents and extended time periods. Using multi-source meteorological, topographic, soil, and remote sensing data for five benchmark years spanning 1985–2024, this study evaluates the long-term ecological effectiveness of the Three-North Shelterbelt Program from an ecosystem services perspective. Four key ecosystem services—water conservation, biodiversity maintenance, soil conservation, and wind erosion control—were quantified to analyze their spatiotemporal dynamics across the Three-North region. The results show that ecosystem services have generally increased over the past four decades, indicating an overall enhancement in ecosystem functioning across much of the study area. Spatially, ecosystem services exhibit a pronounced southeast-to-northwest gradient, with higher service levels in relatively humid southeastern and southern regions and lower levels in arid central and western areas. Analysis across land use types further shows that forest and grassland ecosystems play a critical role in sustaining ecosystem services. In addition, regions with differing levels of ecosystem services require differentiated protection and management strategies. Overall, this study provides a functional-level assessment of long-term ecological changes associated with the Three-North Shelterbelt Program and offers insights to support the design and management of large-scale ecological restoration initiatives in arid and semi-arid regions.</p>