The impact and pathways of changes in land use on carbon emissions in the context of carbon peaking and carbon neutrality （double carbon） were studied from the perspective of transforming farmland into construction land to promote the collaborative governance of ecological environment and achieve the development with green and high-quality. A panel fixed effects model was used to investigate the effects and mechanisms of transforming farmland into construction land on carbon emission based on the data of 224 prefecture-level cities in China from 2009-2010 and 2018-2019. The results showed that the transformation of farmland into construction land across China had a shrinking trend， with the most prominent trend in the eastern and northeastern regions， while the shrinking trend was not obvious in the central and western provinces. The emissions of total carbon only showed a downward trend in the eastern provinces， while other provinces showed an upward trend. The transformation of farmland into construction land significantly increased carbon emissions， and this result remained valid after conducting tests of robustness and addressing issues of potential endogeneity. It is indicated that the changes in industrial structure and energy consumption caused by the transformation of farmland into construction land are the main pathways affecting carbon emissions.