A novel three-dimensional (3D) manganese oxide (MnO_X) hierarchical microflowers materials were prepared and applied to activate peroxymonosulfate (PMS) for the removal of phenol. The 3D α-MnO₂ material exhibited higher catalytic activity than 3D Mn₂O₃ and 3D Mn₃O₄ materials, with 100% phenol removal within 60 min. The quenching experiment and EPR results indicated that ¹O₂ played a major role in removing phenol, SO₄^•–, O₂^•– and ^•OH ranked second. The kinetic studies indicated that the removal of phenol followed the pseudo-first-order kinetic model, and the reaction activation energy of 3D α-MnO₂ material was 25.67 kJ mol⁻¹. Besides, factors of 3D α-MnO₂ catalytic performance such as catalyst dosage, PMS dose and reaction temperature were also investigated. This work provided a new approach for synthesizing 3D MnO_X catalysts with high-performance and guidance for analyzing the catalytic activity of multivalent metal oxides.