An in-depth analysis of China's cropland use carbon source / sink can provide data reference in the field of cropland for the realization of the "double carbon" goal. Taking mainland China as the study area while excluding Hong Kong, Macao, Taiwan, and Tibet because of data unavailability, the carbon emission and carbon sequestration of cropland use in 30 provinces (cities and autonomous regions) of China from2000 to 2019 were calculated. and the net carbon effect was analyzed according to the difference between emissions and sequestration, then its spatial and temporal evolution characteristics were described. Furthermore, the coupling coordination degree and the improved Tapio coupling index were used to explore the relationship between net carbon effect and agricultural output value. The results showed that: (1) In the past 20 years, the average carbon emission of cropland use was 2.33×10⁸ t, rising first and then falling, and reaching the peak of 2.63×10⁸ t in 2015. The sequestration increased from 5.19×10⁸ to 7.86×10⁸ t. Accordingly, the net carbon sequestration rose from 3.19×10⁸ to 5.40×10⁸ t, indicating that the cropland use system in China always displayed an increasing carbon surplus, and the carbon sink effect increased over time. (2) In terms of the temporal characteristics, the net carbon sequestration experienced three stages fluctuating, high speed growth and stable growth. From the perspective of spatial pattern, the net carbon sequestration exhibited gradual decline from east to west. (3) In terms of quantity, the relationship between the net carbon sequestration and agricultural economy evolved from overall imbalance to partial coordination. From the perspective of speed, the growth relationship of the two was in economy-leading coupling in most years, and the provincial coupling status of the two evolved from coexistence of several types to the economy-leading coupling. Consequently, it’s necessary to accelerate the transformation of cropland use mode from agricultural materials driven to technology driven. Besides, we should promote the carbon emission reduction of the whole industrial chain of the planting industry, and promote the emission reduction and the increase of sources in large emission provinces by categories and batches.