A great number of crop straws are produced each year in China. Among all the comprehensive utilizations of crop straw, the method of returning straw to soil has been paied attention and accepted as a recycle technology featuring with increasing the porosity of soil, improving the aggregate structure of soil and increasing the production of crops. The most important indicator to evaluate the effect of straw returning is the decomposition condition of straw. Biochar and digestate were combined as accelerants to expedite the decay of corn stover. The corn stover presoaked with digestate was buried into the soil added with biochar by mesh bag method at room temperature. The experimental process lasted 105d. The decomposition ratio of corn stover and the characteristics of cellulose, hemicellulose, lignin, organic carbon and total cumulative nitrogen were investigated systematically to achieve the effect of biochar on the decomposition characteristics of corn stover presoaked with digestate in soil. The results indicated that the biochar increased the decomposition rate of corn stover significantly. The decomposition condition of corn stover in sandy loam was better than that in loamy soil. The decomposition ratios of comparison samples were 69.96% for the corn stover in loamy soil, 74.63% for the corn stover in loamy soil added with biochar, 78.19% for the corn stover in sandy loam and 79.14% for the corn stover in sandy loam added with biochar, respectively. Furthermore, the decomposition ratio of corn stover was increased as the increase of time. The decomposition rate was fast before 49d and decreased gradually after 49d. The decomposition ratios of cellulose, hemicellulose and total cumulative nitrogen were different significantly (P<0.05). In addition, the decomposition ratio of corn stover was significantly correlated with the decomposition ratio of cellulose (P<0.05). The research result can lay a theoretical foundation for the technology development of returning straw to soil and the comprehensive utilization of biochar.