Abstract: MnFe₂O₄ and a diatomite & MnFe₂O₄ composite catalyst (D&MnFe-50%) were synthesized by the sol-gel method, and their catalytic activities in activating peroxymonosulfate (PMS) for acetaminophen (ACE) degradation were also evaluated. Meanwhile, the impact of preparation conditions on catalyst activity was examined, along with a systematic investigation into the degradation characteristics, influencing factors, and action mechanisms of the catalytic oxidation system. The results show that in the PMS/D&MnFe-50% system, 20 mg/L ACE can be efficiently degraded within 30 min using 0.50 g/L D&MnFe-50% and 0.30 g/L PMS, achieving a degradation efficiency of 98.42%. ACE degradation proceeded effectively over a wide pH range of 3~9, in accordance with the pseudo-first-order kinetic model. The average MnFe₂O₄ grain size is 11.07 nm, with a certain degree of agglomeration. D&MnFe-50% retains the diatomite and MnFe₂O₄ crystal structure and functional groups, and the surface hydroxyl groups of diatomite can facilitate the activation of PMS. After one use, Mn and Fe leached from D&MnFe-50% at concentration of 0.658 mg/L and 0.208 mg/L, respectively. After four cycles, the degradation rate remained as high as 81.80%, demonstrating good reusability. In addition, the analysis reveals that SO₄^-·、·OH、¹O₂ play a dominant role in ACE degradation.