Abstract: Exploring the effects of farmland transfer on agroecological efficiency is of great significance for promoting the efficient and low-carbon utilization of farmland and the green development of agriculture in China. Based on a panel data of 30 provinces in China from 2005 to 2021, and applying the SBM model, this paper calculated the agroecological efficiency of each province, and conducted an empirical analysis of the mechanism of the impacts of farmland transfer on agroecological efficiency by the fixed-effect model, the threshold regression model and the mediating effect model, and identify the mediating effect between the extent of farmland management scale and agricultural mechanization services. Results show that: 1) Agroecological efficiency in China showed an overall upward trend with regional disparities from 2005 to 2021, with eastern region > western region > central region; 2) Farmland transfer greatly enhances agroecological efficiency with a threshold effect. The positive impact on agroecological efficiency decreases when the area of farmland transferred exceeds the threshold; 3) Farmland transfer can improve agroecological efficiency by expanding the scale of farmland management and promote agricultural mechanization services. To improve the agroecological efficiency, this study suggests: accelerating the promotion of the level of farmland transfer; expanding the scale of farmland management, promoting agricultural mechanization services, and paying attention to farmlnad transfer in the western region.