Abstract: Ecological engineering affects the structure and function of ecosystems by changing the quantity and quality of ecological land, which is directly related to the pattern and dynamics of regional ecosystem services. It is very necessary to identify the impacts of ecological engineering construction on regional ecosystem services and then provide useful references for ecological environment construction, especially in agro-pastoral transitional zone. However, there is still a lack of in-depth analysis regarding the impact of the quantity and quality of ecological land on ecosystem services under the implementation of ecological projects. Zhangbei County, a typical county in agro-pastoral transitional zone, was taken as an example, this study aimed to classify and map land use based on Landsat remote sensing images in 2000, 2010 and 2020, by linear spectral mixture model and random forest classification algorithm. The linear spectral mixture model also obtains the abundance values of typical endmembers by decomposing the original image. Three key ecosystem services, including soil conservation, water conservation as well as windbreak and sand fixation, and their evolutionary characteristics were also quantitatively assessed using InVEST model and ArcGIS. The correlation analysis method was then applied to reveal the impact of the quantity and quality of ecological land on the key ecosystem services. The results showed that: 1) The distribution of forestland in Zhangbei County expanded rapidly, with a total increase of 986.10 km² in 20 years, but the areas of arable land and grassland continued to shrink, decreasing by 802.86 km² and 307.43 km² in 20 years, respectively. It was worth noting that there was a certain spatial overlap between the expansion of forestland and the shrinkage of arable land and grassland. Soil conservation, water conservation and windbreak and sand fixation in Zhangbei County as a whole showed an overall strengthening trend. However, there was obvious spatial heterogeneity in the specific distribution. 2) With regard to changes in the quantity of ecological land, the total area of ecological land has been continuously increasing, increasing by 687.67 km ² over the past 20 years. Among them, the increases in the area of forestland, grassland and their total area had a significant effect on soil conservation and water conservation services, while only the increase in the area of forestland had a positive impact on windbreak and sand fixation. In terms of changes in the quality of ecological land, during the 20-year period, the average abundance values of endmember elements in forestland declined by 0.108, with an overall decreasing trend, while the average abundance values of endmember elements in grassland increased by 0.099, with an overall weakly increasing trend. The improvements in the quality of forestland and grassland enhanced soil conservation, water conservation and windbreak and sand fixation, whereas windbreak and sand fixation was the most sensitive to changes in the quality of forestland and grassland. The results offer a new cognitive perspective for exploring the impact of ecological engineering construction on ecosystem services, while also providing region-specific policy insights for ecological restoration in agro-pastoral transitional zone. In future research, the impact of fine classification of ecological land on ecosystem services should be further examined. Additionally, it is necessary to incorporate time-series data of climatic factors into vegetation ecological process models to reveal the feedback effects of ecosystem services on climatic factors. This approach will help distinguish the relative contributions of climatic factors and ecological engineering to regional ecosystem services.