Abstract: Carbon footprint is an indicator used to measure the amount of carbon dioxide emissions directly or indirectly caused by individuals, organizations, products, or countries over a certain period of time. The research on carbon sources/sinks in agricultural ecosystems at the municipal level in China is not sufficient, and the time span is narrow. In the calculation process, important parts such as N₂O in farmland, CH₄ in rice fields, soil respiration or carbon sequestration are even ignored, which cannot accurately reflect the carbon source/sink status of regional ecosystems. This article takes the farmland ecosystem in Heihe City as the research object. Based on statistical data such as crop sowing area, yield, and agricultural production input from 1984 to 2023, a carbon footprint model is constructed to estimate the total carbon source/sink of the farmland ecosystem in Heihe City. The temporal variation characteristics are analyzed, and on this basis, targeted suggestions for carbon sequestration, emission reduction, and sustainable green development of the farmland ecosystem are proposed. The results show that: (1) the carbon emissions of farmland ecosystems in Heihe City increase over time, and their absorption and carbon footprint exhibit volatility; (2) Tillage and fertilizer use are the main sources of carbon emissions; (3) Soybeans, corn, and wheat are the main carbon absorbing crops: (4) The agricultural ecosystem plays a carbon sink role, and the agricultural ecosystem in Heihe City shows a carbon ecological surplus.