In this study, rice straw biochar modified with Co3O4-Fe3O4 (RSBC@Co3O4-Fe3O4) was successfully prepared via calcinating oxalate coprecipitation precursor and employed as a catalyst to activate peroxymonosulfate (PMS) for the treatment of Rhodamine B (RhB)-simulated wastewater. The results indicated that RSBC@Co3O4-Fe3O4 exhibited high catalytic performance due to the synergy between Co3O4 and Fe3O4 doping into RSBC. Approximately 98% of RhB (180mg/L) was degraded in the RSBC@Co3O4-Fe3O4/PMS system at initial pH 7 within 15min. The degradation efficiency of RhB maintained over 90% after the fourth cycle, illustrating that RSBC@Co3O4-Fe3O4 displayed excellent stability and reusability. The primary reactive oxygen species (ROS) answerable for the degradation of RhB were 1O2, •OH, and SO4•-. Moreover, the intermediates involved in the degradation of RhB were identified and the possible degradation pathways were deduced. This work can provide a new approach to explore Co-based and BC-based catalysts for the degradation of organic pollutants.