Intelligent polymer was extendedly applied to fabricate a novel environmentally responsive Fenton catalyst in this study. The obtained magnetite/sodium carboxymethyl cellulose-graft-poly(acrylic acid) (Fe3O4/CMC-g-PAA) nanocomposites showed perfect superparamagnetism, pH response, and superior catalytic activity. In a wide range of pH (3-9), the highly swollen polymer coating not only favored the dispersion of Fe3O4 nanoparticles and protected them from leaching but also promoted interface mass transfer with large amounts of hydrophilic ingredients.