Abstract: Soil acidification is one of the important manifestations of soil degradation, and it is easy to cause many problems, such as soil hardening, fertility decline, heavy metal mobility enhancement, biological activity reduction, crop yield and quality decline and so on. In recent years, with the rapid development of modern society, the continuous interference of high-intensity human activities and other factors, soil acidification has become more and more serious, which has seriously affected the quality of soil ecological environment and seriously restricted the soil productivity. Biochar has the characteristics of high pH value, developed pore structure, huge specific surface area, excellent adsorption performance and rich elements. Therefore, it has attracted the attention of domestic and foreign scholars in acid soil improvement. This paper reviews the effects of biochar application on the physical and chemical properties of acid soil, soil microorganisms, soil enzyme activities, crop yield and quality, and discusses the possible mechanism. Finally, the unsolved problems of biochar in acid soil improvement are put forward and prospected in order to provide references for the theoretical research and application of biochar in improving acid soil.