Abstract: Soil acidification is one form of farmland soil degradation and poses a threat to crop production. Under natural conditions, soil acidification is a relatively slow process. However, anthropogenic activities, such as acid deposition, especially excessive fertilization and improper farming managements have accelerated acidification process. This review elucidates the fundamental principles behind soil acidification, assesses the research findings from long-term field experiments on soil acidification in different countries or regions, and analyzes the trend of acidification of farmland soils in China. The paper summarizes the adverse effect of soil acidification on different types of agricultural soils regarding soil microorganisms, soil physicochemical properties, and crop growth. The results of different control experiments are integrated and effects of alkaline soil amendments, biochar, and organic fertilizers in mitigating soil acidification are discussed. Meanwhile, possible research avenues on soil acidification in farmland which need to be strengthened are prospected.