Abstract: In order to better deal with the problem of azo dye (acid orange, AO7) dye pollution in water environment, Mn and N co-doped biochar composites (Mn-N-BC) were prepared by pyrolysis method using rice husk, urea and manganese salt as raw materials, and acid orange (AO7) dye wastewater was degraded by activated peroxydisulfate (PDS). The effects of initial AO7 concentration, PDS concentration, catalyst dosage and initial pH value on the removal rate of AO7 were investigated. The results show that the Mn-N-BC/PDS system has a high removal rate of AO7 dyes, which can reach 98.6% in 30 min, its apparent rate constant k_obs is 0.125 min⁻¹; and shows high resistance to inorganic anions in the water environment. After three times of recycling, the removal rate of AO7 is still about 75%, indicating that Mn-N-BC has high reusability and stability in the removal of organic pollutants. Free radical quenching and XPS analysis showed that the degradation mechanism of AO7 in Mn-N-BC/PDS system included free radical pathway (•OH, SO₄⁻•) and non-free radical pathway (O₂⁻•, ¹O₂ and electron transfer), in which non-free radical pathway was the main role.