The protection of cultivated land is related to food security and sustainable agricultural development. Improving agricultural planting efficiency and reducing chemical inputs are important to promoting sustainability and protecting cultivated land, and agricultural mechanization plays an important role in this process. Based on the survey data of 2118 households in 10 provinces of China, we used the Oprobit and IV-Oprobit models to analyze the impact and mechanism of agricultural mechanization on the behaviors of farmers in achieving sustainability and protecting cultivated land. The results show that agricultural mechanization has a significant promotion effect on the behaviors of farmers, especially in motivating them to adopt higher levels of protective behaviors in terms of sustainable land cultivation. At the same time, the impacts of agricultural mechanization on the different production links were different. The promotion effect of the harvesting link on the sustainability protection behaviors of farmers was the most obvious, and the promotion effects of the tillage and sowing links were the least obvious. In addition, planting income and fertilizer input played a role in mediating between mechanization and cultivated land sustainability protection. Further analysis showed that agricultural mechanization can more effectively motivate farmers with full-time businesses or higher land concentrations to prioritize cultivated land sustainability. Therefore, it is necessary to pay attention to the role of agricultural mechanization in promoting sustainability, protecting cultivated land, and promoting innovative green agricultural machinery. Via mechanization, we can increase the incomes of farmers, reduce excessive fertilizer use, and specifically target full-time farmers engaged in agricultural production and key aspects of land sustainability protection to promote the construction of better agricultural machinery systems, as well as agricultural machinery research and innovation, thereby fully leveraging the ecological protection effects of agricultural mechanization.