Abstract: The combined Fenton/flocculation process produces a large amount of Fenton sludge when treating refractory organic wastewater, which increases the cost of wastewater treatment and poses a threat to the environment. It is urgent to develop a green and sustainable method to achieve the resource utilization of Fenton sludge. The disposal of Fenton sludge often leads to secondary pollution. Sludge pyrolysis appears to be less polluting than traditional methods and has received increasing attention from domestic and foreign scholars. In this study, magnetic biochar (MBC) with high catalytic activity was prepared in situ by co-pyrolysis of Fenton sludge produced by the treatment of p-nitrophenol (PNP) wastewater and biochemical sludge from a sewage plant, and a heterogeneous Fenton catalyst was used to remove PNP in what can be considered as "treating waste with waste". The results showed that: the best performing catalytic (named MBC-800-3) was obtained when the mass ratio of Fenton sludge to biochemical sludge was 1:1 and the pyrolysis temperature was 800 ℃. This mixing ratio effectively avoided particle aggregation, while the high temperature formed defective structures and various iron phases, that provided rich reactive sites on MBC-800-3. When the initial pH of the wastewater was 3, the H₂O₂ concentration was 60 mmol/L and the MBC-800-3 dosing was 0.4 mg/L, the removal rates of PNP and total organic carbon were the highest at 100 min of catalytic reaction, reaching 98% and 62%, respectively. Under acidic conditions, MBC activated H₂O₂ to produce ·OH and ·O₂^- that catalyzed the degradation of organic matter in wastewater. Among them, ·OH was the main active species, and the sources included both homogeneous and heterogeneous Fenton reactions. The study shows that MBC-800-3 has high catalytic activity as well as good stability and regeneration, thereby exhibiting good application potential, which is of significance for the resource utilization of Fenton sludge.