Abstract: Biochar is a kind of soil improvement and remediation material with high carbon content, specific surface area, porosity and adsorption properties. It can influence the soil through physical, chemical and biological ways, but the influence and mechanism vary with soil properties and biochar types. The composition, specific surface area and porosity, pH and surface functional groups of biochar and the raw materials and charring technology of the biochar were summariezed. Effects of biochar addition on soil structure improvement, soil fertility improvement, soil pH regulation, contaminated soil repairment, biological activity enhancement and nutrient transformation promotion were comprehensively generalized. It was found that the soil was remediated or improved by biochar mainly through filling and expansion, pore interception, cementation and coagulation, physical adsorption, chemical adsorption, ion exchange, coordination and complexation, coprecipitation, microbial mediation and so on. The effects and mechanism of biochar on soil were clarified from physical, chemical and biological aspects, respectively. The modification and charring technology of biochar, the proportion of mixed application of biochar and the environmental risk assessment after biochar application in the future should be the key research contents.