Trimethylphenol is an organic toxic byproduct of industrial process, which is difficult to be eliminated through conventional degradation without harsh conditions. In this work, a sulfite-based oxidation process activated by ZnO-embedded hydrogel was studied for the degradation of 2,4,6-trimethylphenols in the ambient conditions. The ZnO/Na₂SO₃ oxidative system can effectively degrade trimethylphenol via the generation of radicals such as SO₄^·−, OH^·, and SO₃^·−. The presence of hydrogel matrix facilitates the distribution and recyclability of ZnO catalysts while maintaining high degradation kinetics and little leaching of metal ions. Results suggest the promising potential of ZnO-hydrogel in wastewater treatment with good performance in terms of pH sensitivity, anion interference, recyclability, etc. The combination of ZnO catalysts, hydrogel, and sulfite-based advanced oxidation process may provide essential support for the current treatment of alkylated phenols with strong potential in the commercial scale-ups.