Abstract: Using sugarcane bagasse as raw material, the microwave method was applied for the synthesis of Fe₃O₄ magnetically modified bagasse. Then a chemical modification was followed by the use of citric acid, and finally a kind of biomass adsorbent which could be quickly and easily separated and had good adsorption effect was prepared for removal of malachite green in simulation wastewater. The removal effect of malachite green between bagasse before and after modification was compared, and the structure and components of the two kinds of materials were characterized by SEM and FTI. The adsorption mechanism was explored applying adsorption kinetics experiment and equilibrium experiment, and the influence of the temperature, pH and adsorbent dosage on the adsorption tested. The result shows that the adsorption process conforms to the Pseudo-second order kinetic model and the Langmuir model. For 50 mL malachite green solution with the initial concentration of 20 mg/L, under the pH of 7.5 and the temperature of 50 ℃, the removal rate of 98% could be reached by adding 15 mg of sorbent. The adsorption amount was 140.2 mg/g, nearly double of that by bagasse with no modification.