Abstract: To meet the needs of food security, ecological security and urban development, the Chinese government proposed the system of Requisition-Compensation Balance to swap the spatial position between farmland, forest land and construction land. However, this system also makes a large amount of farmland abandoned, which has violated China's policy of "Hiding Grain in the Land". The methods of binary logic regression model and grain capacity accounting model were used to analyze the phenomenon, causes, and grain productivity effects of farmland abandoned in Wannian County, a mountainous agricultural county. The study found that: (1) From 2010 to 2020, the supplementary farmland in Wannian County has been uphill and fragmented, and the abandonment rate has reached about 14.77%. (2) The farmland is more likely to be abandoned when its altitude>130 m and patch area<0.2 hm², or permanent population density of the located village <400 people/km2 and patch area<0.2 hm², or patch area<0.2 hm² and traffic distance with adjacent farmland＞40 m, or altitude>110m and traffic distance with adjacent farmland＞70 m. (3) 3 183.39 hm2 of forest land can be reclaimed in county areas, of which forest land, other forest land, and sparse forest land account for 88.25%, 9.74% and 2.01% respectively. (4) The replacement of farmland and sparse forest space can make up for the loss of 297.48 t production capacity caused by the abandonment. The study has shown that the abandonment of farmland is the result of spatial mismatch caused by the coupling relationship between land use conditions-state-functions.Therefore, we put forward joint strategies of requisition-compensation balance among farmland, forest land, and construction land in mountainous areas, so that the farmland uphill can be swapped to the place suitable for cultivating by humans.