Using Na2S2O3 as sulfur source, a series of sulfur-modified porous Co3O4 catalysts with different sulfur contents were prepared by an improved oxalate-pyrolysis method (Sx@Co3O4, x=0.25, 0.5, 0.75, 1, where x represented the added ratio of sulfur and was calculated by the amount of Co(NO3)2?6H2O). Their properties for activating peroxymonosulfate (PMS) to degrade methylene blue (MB) were compared and the catalyst with the best catalytic performance was screened out. On this basis, the influences of treatment parameters including catalyst dosage, PMS concentration, reaction temperature and common anion species on MB degradation ratios under Sx@Co3O4-PMS system were investigated. Besides, the cyclic stability of catalyst was evaluated. Results showed that the performance of Co3O4 was boosted with the increase of sulfur content in the range of this study, and S1@Co3O4 exhibited the best catalytic performance. Moreover, it was confirmed that sulfur element was uniformly bonded on the surface of Co3O4 in the form of SO42-. The modification of S increased the specific surface area, oxygen vacancy content of Co3O4 and enhanced the polarization effect for HSO5-, which was considered as a key reason for improving the catalytic activity of Co3O4. Under the optimal reaction conditions: catalyst dosage of 0.04 g/L, PMS concentration of 0.6 mmol/L, reaction temperature of 25 ℃, and reaction time of 25 min, a degradation rate of 98.35% for MB (500 mL 10 mg/L) could be reached in the S1@Co3O4-PMS advanced oxidation system. S1@Co3O4 was recycled in a simple way and the degradation ratio of MB could reach 68.57% after four consecutive cycles. Furthermore, electron paramagnetic resonance spectroscopy (EPR) confirmed that the degradation of MB in S1@Co3O4-PMS system was the result of co-action of free radicals (?SO4-, ?OH and ?O2-) and non-free radicals (1O2).