The electro-Fenton process with a dimensionally stable anode and a graphite felt cathode was applied to the oxidative degradation of the antibiotics levofloxacin and trimethoprim. The comparison of electron spin resonance spectra for the catalysts Pd-Fe3O4 and Fe3O4 verified that Pd loading contributed to the coexistence of "OH and atomic H* in the electro-Fenton process. The use of Pd-Fe3O4 instead of Fe304 showed evident superiority for the degradation of levofloxacin according to the increased apparent rate constant value from 0.156 to 0.243 min(-1), whereas it was almost unchanged (0.041 min(-1)) for trimethoprim. Moreover, the total organic carbon abatement after 8 h treatment confirmed the superiority of Pd-Fe3O4 attaining the almost complete mineralization of levofloxacin, and the mineralization current efficiency suggested that atomic H* weaken the recalcitrant intermediate of levofloxacin more efficiently compared to trimethoprim. The modelling study indicated that the dispersion of Pd particles on the surface of Fe3O4 promoted the d-band center due to more exposure active sites. The structure calculation of antibiotic and typical intermediates is in agreement with the comparison of experimental results, proposing a theoretical approach to evaluate antibiotic wastewater. The calculation of antibiotic structure and modelling study of catalyst were firstly combined to clarify the structure-based synergistic mechanism between the nucleophilic and electrophilic radicals. (C) 2018 Elsevier Inc. All rights reserved.