Abstract: Fe-N/biochar was prepared by microwave pyrolysis combined with a hydrothermal method using rapeseed straw as biomass raw material mixed with different proportions of boric acid (m (boric acid)∶m (straw)=1∶1 and m(boric acid)∶m(straw)=2∶1). The morphology and structure of the materials were characterized by XRD and SEM, and the property differences of biochar prepared with different ratios of boric acid were studied. The degradation efficiency of 50 mg/L methylene blue by the Fenton system of biochar at different H₂O₂ concentrations and ambient temperatures was compared and analyzed by the control variates. The results showed that such degradation performance of biochar pyrolyzed by m(boric acid)∶m (straw)=2∶1 was better than that by m(boric acid)∶m(straw)=1∶1 under various reaction conditions. The optimal H₂O₂ concentration for degradating methylene blue solution was 5 mmol/L at 25 ℃ and pH=3. With increasing reaction temperature, the degradation efficiency of methylene blue increased gradually.