In this work, monochlorophenols (MCPs) isomers degradation was investigated by Co-doped g-C3N4 (CCN) using peroxymonosulfate (PMS) as the oxidant. The effects of the doping amount of Co, the concentration of PMS, the loading of catalyst and initial pH of the solution on the catalyst activity were systematically studied. The results showed that MCPs could be degraded effectively by CCN/PMS system. The degradation reaction followed pseudo-first order kinetics. Sulfate radical (SO4-) was found as the major active radicals in the degradation process. MCPs were degraded effectively with the degradation rate order of 2-chlorophenol (2-CP) > 3-chlorophenol (3-CP) > 4-chlorophenol (4-CP). Except for the influence of structural characteristics of MCPs, this degradation rate order was also related to the adsorption behavior of CCN, which was based on the intermolecular interaction. Based on the analysis of the degradation products of MCPs, 1,4-benzoquinone or chlorinated 1,4-benzoquinone had been found to be the main intermediates.