<p>A hierarchical porous polystyrene microsphere (HPPM) that simultaneously possesses micro-, meso-, and macropores was fabricated by two-step seed swelling and hyper-crosslinking method, respectively, based on the polystyrene (PS) microspheres prepared by dispersion polymerization using a shaker. Subsequently, Au NPs were in-situ loaded onto the sulphonated HPPM via a thermal reduction reaction to prepare the hierarchical porous polystyrene microsphere-supported Au NPs (Au@sHPPM) composite catalyst. SEM and particle size test results show that the microspheres exhibit excellent monodispersity. The specific surface area reaches 529.21 m²·g⁻¹ when the ratio of St/DVB is 0.6:2.0, and further increases to 644.14 m²·g⁻¹ after hyper-crosslinking. The XRD and XPS analysis results indicate that HAuCl₄ is reduced to Au NPs. In the reduction reaction of 4-nitrophenol with sodium borohydride (NaBH₄), Au@sHPPM composite catalyst demonstrates excellent catalytic performance, with a conversion rate of up to 96.76% within 15 minutes. Furthermore, it also demonstrates outstanding catalytic performance for organic dyes such as Congo red, Rhodamine B and Malachite green, indicating that the Au@sHPPM composite catalyst has good stability and reusability.</p>