Based on the micro-survey data of agricultural production of 795 farmers in 100 villages of five provinces of China, this article useslife cycle assessment method to calculate the carbon emissions of farmers’ crop planting, and explores the relationship between the scale of farmers’ land transfer-in, land operation scale and the carbon emissionsintensity of crop planting. The results show that in 2018, the carbon emission intensity of Chinese farmers’ crop planting was 334.12kg CO2-eq/mu, with obvious regional differences. The expansion of farmers’land operation scale has generated carbon reduction effect, but it has been inhibited by land transfer-in scale. The heterogeneity analysis shows that the higher the average education level of household members and the lower their dependence on agriculture, the weaker the inhibition effect of land transfer-in scale on carbon reduction effect of land operation scale. The carbon reduction effect of the expansion of land operation scale and the inhibition effect of the expansion of land transfer-in scale mainly occurred in farmer groups with smaller land operation scale. From the perspective of whether to pay land rent, the impact of land transfer-in scale on carbon emissions of crop planting is notstatistically significant for farmers who pay land rent. In terms of different crops, the carbon reduction effect of the expansion of land operation scale and the inhibition of the expansion of land transferscale on the carbon reduction effect mainly occur in rice planting. The mechanism analysis showsthat the expansion of land transfer-in scale mainly suppresses the carbon reduction effect of the expansion of land operation scale by increasing fertilizer inputs and adjusting planting structure. Based on the conclusions, the study proposes the necessity to pay more attention to the inhibition of the carbon reduction effect of the expansion of land transfer-in scale, guide scientific fertilization and rational adjustment of planting structure, and focus planting carbon emission reduction policies on smallholders.

通讯作者：Jianbing Guo，bjfuguojian@163.com