With the intensification of human activities, soil acidification has become a very serious threat to crop yield and food security. From a practical application perspective, this study used biochar to improve acidified soil. The concept of molded soil was put forward to examine the soil improvement effect of biochar. The changes in soil hydrological parameters suggested that biochar application improved the structure of acidified soil. The volumetric water content and vertical permeability coefficient of soil were improved to different degrees. In addition to increased soil moisture content due to biochar adsorption of soil micro-aggregates, biochar application improved the oxidation stability of soil organic carbon and promoted the formation of water-stable macro-aggregates. The molded soil showed little difference with acidified soil and was found representative and suitable for indoor small-scale regular exploratory experiments. This study found that leaching may promote the migration of acidic ions enhancing the biochar improvement efficiency of acidified soil, however, the phenomenon needs further study. This study provides theoretical support for acidified soil water retention, fertilizer conservation, obstacle elimination, productivity improvement of farmland, and reduction of groundwater non-point source pollution.