Abstract: Agricultural mechanization is essential for achieving agricultural modernization, while enhancing agricultural eco-efficiency is a critical step toward advancing rural ecological civilization. A thorough investigation of the relationship between agricultural mechanization and eco-efficiency holds significant practical implications. This study begins with a theoretical analysis of the linkage between agricultural mechanization and eco-efficiency. Subsequently, using provincial panel data in China from 2005 to 2021, we employ a global reference Slack-Based Measure (SBM) model with undesirable outputs to estimate regional agricultural eco-efficiency. Finally, we develop an econometric model to empirically examine the effects of agricultural mechanization on eco-efficiency. The results indicate the following: Firstly, while the overall agricultural eco-efficiency in China showed an upward trend during the sample period, the levels of agricultural eco-efficiency in most provinces remained relatively low, with significant potential for improvement. Secondly, agricultural mechanizaton has a statstically significant positive impact on agricultural eco-efficiency. The mechanism analysis reveals that agricultural mechanization exerts a positive mediating effect on agricultural eco-efficiency through two pathways: grain production increases and growth in agricultural productive services. Thirdly, the impact of agricultural mechanzation on agricultural eco-efficiency exhibits a double-threshold effect based on the rural land transfer rate. When the rural land transfer rate is below the first threshold value, agricultural mechanization significantly impedes agricultural eco-effciency. When the rural land transfer land is between the first and second threshold values, agricultural mechanizaton has a signficantly positive effect on agricultural eco-efficiency. When the rural land transfer rate exceeds the second threshold value, the positive impact of agricultural mechanization on agricultural eco-efficiency is further enhanced. Fourthly, the heterogeneity analysis shows that agricultural mechanization has a more pronounced promoting effect on agircultural production efficiency in regions with larger geographic slopes, non-grain production areas, higher levels of agricultural mechanizaton, and lower levels of agricultural eco-efficiency. This study offers theoretical insights and policy recommendations for advancing agricultural mechanization and eco-efficiency enhancement.