Using corn straw as raw material of biochar and modified with chitosan and rare earth, chitosan?lanthanum chloride?biochar composites and chitosan?cerium chloride?biochar composites were prepared respectively. The structure and performance of CBC?La and CBC?Ce were analyzed by XRF, FT?IR and XRD. The adsorption properties of Cr(Ⅵ) in water under different adsorption conditions were investigated. The experimental results show that the Langmuir equation can simulate the isothermal adsorption behavior well, and the quasi?first?order kinetic equation has a higher fitting degree. The theoretical equilibrium adsorption capacity are 21.08 mg/g and 19.16 mg/g, which is close to the actual value. The desorption experiments show that CBC?La and CBC?Ce had the possibility of reuse. The adsorption mechanism mainly includes electrostatic adsorption, complexation and ion exchange. The experimental results show that the chitosan?rare earth?biochar composite material has a good application prospect in the removal of Cr(Ⅵ) from water.