A novel core-shell structured Fe3O4@GO@MIL-100(Fe) magnetic catalyst was successfully synthesized and used as heterogeneous photo-Fenton catalyst for 2,4-dichlorophenl (2,4-DCP) degradation. The catalyst was fully characterized by X-ray diffraction pattern (XRD), Raman spectroscopy, Scanning electron microscopy (SEM), Transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Brunner-Emmet-Teller (BET) and magnetic hysteresis loops measurements. The effects of initial pH, H2O2 concentration, catalyst load and irradiation intensity on 2,4-DCP degradation were also investigated. The results showed that Fe3O4@GO@MIL-100(Fe) exhibited excellent photo-Fenton catalytic activity, achieving almost 100% of 2,4-DCP degradation within 40 min at reaction condition of 3 mmol/L H2O2, 50 mg/L 2,4-DCP, pH 5.5 and irradiation intensity of 500 W. The high catalytic activity of Fe3O4@GO@MIL-100(Fe) can be attributed to the efficient transfer of photo-generated electrons between MIL-100(Fe) and Fe3O4 by GO. The recycling experiments displayed that Fe3O4@GO@MIL-100(Fe) catalyst possessed good stability and could be easily recovered under an applied magnetic field. Finally, the possible mechanism of 2,4-DCP degradation in the photo-Fenton system catalyzed by Fe3O4@GO@MIL-100(Fe) was also proposed according to the analyses of reactive species, photoluminescence (PL) emission spectra and the photocurrent responses.