Abstract: In this paper,the fixation effect and passivation mechanism of straw biochar and phosphorus-containing substances on heavy metals in soil were reviewed,including precipitation-complexation,electrostatic adsorption and ion exchange.The influence of biochar application amount on the presence form of heavy metals in soil was explored,and the factors affecting the passivation of heavy metals were summarized,including biomass raw materials and their pyrolysis temperature,soil pH value and organic matter.The level of H⁺ content would affect the adsorption site of biochar for heavy metals,and the high concentration of H⁺ was competitive with the adsorption site of materials.The high concentration of OH^- promotes the fixation of heavy metals in the form of precipitation.The high content of organic matter will increase the cation exchange capacity and produce ion exchange reaction with heavy metals.The batch adsorption of heavy metals by straw biochar and modified substances conforms to Langmuir and quasi-second-order kinetic model.The effects of different biochar contents and materials on the forms of heavy metals were introduced in this paper.The negative effects of long-term use of biochar on soil environment.