The invention belongs to the technical field of restoration and treatment of heavy metals in soil, and discloses a high magnetic modified biochar, a preparation method of the high magnetic modified biochar, and an application to treatment of the heavy metal pollution to the soil. The preparation method comprises the following steps: grinding and sieving the biochar, adding the biochar into a NaOHsolution, stirring, filtering, and washing with water; adding a filter residue into an HCl solution, continuing to stir, filtering, washing with water to obtain a basic charcoal material, and drying for later use; adding the basic charcoal material into an FeCl2-7H2O aqueous solution, regulating the pH value, adding a sodium borohydride solution until no bubble is generated, then adding a saturated sodium dimethyl dithio carbamate aqueous solution, continuing to stir, collecting a residue in the solution through a magnetic field, and washing and drying to obtain the high magnetic modified biochar. The specific surface area of the modified biochar is increased, the passivating efficiency of the heavy metals in the soil is improved, the magnetic property of the high magnetic modified biocharis strong, the high magnetic modified biochar is removed from the soil through a magnet, and the total content of the heavy metals in the soil is reduced.