Flexible governmental intervention is a pivotal mechanism for advancing carbon emission reductions. However, the ramifications of governmental interventions on agricultural carbon emissions still need to be adequately elucidated. This study systematically explores the impact of fiscal expansion on agricultural carbon emissions. The results show that: (1) There is a positive correlation between fiscal expansion and agricultural carbon intensity, which mainly promotes the decline of agricultural carbon intensity by improving agricultural green total factor productivity. However, no empirical evidence exists that would prove fiscal expansion reduces total agricultural carbon emissions. (2) The U-shaped relationship between fiscal expansion and agricultural carbon intensity is significant in non-main grain-producing areas but not significant in main grain-producing areas. (3) The agricultural carbon emission reduction effect of fiscal expansion is limited by the degree of market segmentation, deviation of industrial structure, and economic growth pressure. Our research highlights government intervention’s important role and optimization path in reducing agricultural carbon emissions.