Abstract: Agricultural mechanization has led to increased energy consumption in agriculture, which has become a widely discussed factor restricting China’s agricultural carbon peak. However, what is often overlooked is that agricultural mechanization also results in the reallocation of agricultural inputs, such as chemicals, and adjustments in crop planting structures, which in turn introduce uncertainties into changes in China’s agricultural carbon emissions. This study provides a detailed analysis of the impact of agricultural mechanization on China’s agricultural carbon peak by clarifying these pathways. Based on county-level data across the country (not including Hong Kong, Macao, Taiwan and Xizang of China), this study empirically analyzed the impact of agricultural mechanization on agricultural carbon emissions in China using a fixed effects model. Furthermore, a simultaneous equations model was employed to empirically test the pathways of this effect from the perspectives of chemical inputs and rice planting. The research findings indicated that 1) with the increase in the intensity of agricultural machinery utilization intensity, agricultural carbon emission intensity first increased and then decreased in an inverted U-shape, with the turning point occurring when the machinery utilization intensity reached 87.50 kW∙hm⁻², much higher than the current national average level; 2) as the machinery utilization intensity increased, the intensity of agricultural chemical inputs, such as fertilizers and pesticides, followed a similar inverted U-shape pattern, becoming the dominant factor driving the inverted U-shape trend in agricultural carbon emission intensity; 3) as the machinery utilization intensity increased, the proportion of rice planting area initially decreased and then increased in a U-shape; however, this was not sufficient to reverse the inverted U-shape trend of agricultural carbon emission intensity. Therefore, in the early stages of agricultural mechanization, the intensity of agricultural carbon emissions increased, thereby restricting the agricultural carbon peak. However, when machinery utilization intensity reached a certain level, it contributed to a reduction in agricultural carbon emissions. This inverted U-shaped trend was mainly due to similar changes in the agricultural chemical input intensity. Based on these findings, accelerating the process of agricultural mechanization to promote agricultural carbon reduction while enhancing the environmental management of agricultural chemicals and optimizing agricultural production structures in the early stages of mechanization to drive further carbon reduction in agriculture is crucial.