A novel photo-catalytic system composed of N -doped biochars (NBCs), MnFe2O4 and sulfite activation under ultraviolet (NBCs/MnFe2O4/ sulfite/UV) was constructed to realize the efficient eliminate of tetracycline (TC). As the carrier of MnFe2O4, NBCs were synthesized from alfalfa, which has large specific surface area, graphite like structure and hierarchical porous structure. The adsorption isotherm indicated that NBCs/MnFe2O4-2:1 had the best adsorption performance for TC (347.56 mg g-1). Through synergistic adsorption and photocatalysis, the removal rate of TC reached 84%, which was significantly higher than that of MnFe2O4. Electrochemical impedance spectroscopy (EIS) and Photoluminescence (PL) characterization results showed that the introduction of NBCs improved the separation efficiency of photogenerated electron and hole pairs and enhanced the photocatalytic performance. Moreover, the adsorption, degradation mechanism and degradation path of TC by the catalyst were systematically analyzed by coupling HPLC-MS measurement with the theoretical calculation. Considering the advantages of excellent degradation performance, low cost, easy separation and environmental friendliness of NBCs/MnFe2O4, this work was expected to provide a new path for the practical application of biochar. (c) 2022 Institute of Process Engineering, Chinese Academy of Sciences. Publishing services by Elsevier B.V. on behalf of KeAi Communications Co., Ltd. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).