Three preparation methods of magnetic biochar were introduced. The mechanism and influencing factors of magnetic biochar adsorbing heavy metals were summarized. The application of magnetic biochar was described. The analysis showed that the influence of raw materials for preparing biochar on adsorption performance was related to the structure of biomass. The existing forms of heavy metal ions and surface charge of biochar were significantly affected by the solution pH. With the increase of pyrolysis temperature, the specific surface area and porosity of biochar increased, but the pyrolysis yield of biochar decreased. After magnetic modification, the specific surface area of biochar, the types and quantities of surface functional groups increased, which could significantly improve the removal efficiency of heavy metal ions. Moreover, biochar could be easier to separate from aqueous solution after magnetic modification.