Based on the special molecular structure of surfactant, paramagnetic material used as magnetic nucleus was coated with two layers of surfactant including an inner layer and an outer layer. Magnetic reagent can combine with activated carbon due to adsorption of hydrophilic raclical of the outer surfactant layer. So activated carbon has magnetism. The effects of magnetic reagent dosage pH and activator upon the magnetic susceptibility of activated carbon were studied. Concerning the optimal conditions. MR-20 is the best magnetic reagent. Concentration of CaCl2 is 0.02M and pH 1.8–2.4. The physical properties of magnetic activated carbon vary with the types, dosage and magnetizing condition of magnetic reagent.