Abstract: The reduced graphene oxide (RGO) has been widely used in the treatment of oil, heavy metal ions, organic dyes and other fields due to the large specific surface area, high electron transport efficiency and fast adsorption rate. However, the poor dispersion caused by agglomeration limited the further research. In-situ polymerization was used to prepare nano core-shell polystyrene aldehyde microspheres (PS-CHO)@RGO composite microspheres. The morphology and physicochemical properties of the PS-CHO@RGO composite microspheres were characterized by TEM, Raman, XRD, XPS and insulation resistance tester. The methylene blue (MB) was selected as the target pollutant, the oxidation activity of PS-CHO@RGO composite microspheres in the presence of potassium hydrogen persulfate (PMPS) was investigated, and the degradation mechanism was proposed. The results indicate that RGO layer is uniformly coated on the surface of PS-CHO microspheres, which effectively improved the dispersion. The prepared PS-CHO@RGO composite microspheres are described as low penetration threshold and perfect conductive network. In the degradation experiment, PS-CHO@RGO composite microspheres can stimulate PMPS to generate sulfate radicals (SO₄⁻•), over 98% of MB is catalytically degraded within 60 minutes. Meanwhile, the PS-CHO@RGO composite microspheres also show good stability and can be recycled by high-speed centrifugation.