Novel Fe3O4-CsxWO3/NiAl layered double hydroxide composites (FCW/LDH) for the activation of peroxymonosulfate (PMS) and the succeeding degradation of 2,4-dichlorophenoxyacetic acid (2,4-D) was synthesized through a simple method. The composites prepared were characterized by XRD, SEM, EDS, FT-IR, UV-vis DRS, and N-2 physisorption, respectively. It was found that FCW/LDH could effectively catalyze PMS to generate sulfate radicals (SO4 center dot-) to degrade 2,4-D. The added 2,4-D (20 mg/L) was almost completely removed (with a removal of 90.53%) in 180 min by using 1.00 g/L FCW/LDH and 0.50 g/L PMS. Several related factors (PMS concentration, initial pH, disturbing anions) were tested in order to understand their effect on the degradation performance. Furthermore, the photocatalysts exhibited good reusability and stability after four recycles. Finally, a possible degradation mechanism was provided according to the above experimental results. The desired FCW/LDH composites showed promising application in purifying water.