Porous nitrogen-doped reduced graphene oxide (NRGO) is successfully synthesized from graphene oxide via the combination of CO activation and nitrogen doping with ammonia. The performances of the carbon materials are evaluated by catalytic activation of perroxymonosulfate (PMS) for phenol degradation. The effect of the treatment sequence of CO activation and nitrogen doping on the catalytic activity of the derived product is investigated. The material obtained by CO activation-nitrogen doping (P-NRGO) shows better activity than the one obtained from nitrogen doping-CO activation (N-PRGO). The activation mechanisms are also investigated by radical scavenging test, and the P-NRGO/PMS system is unveiled to rely on the nonradical oxidation pathway. The turnover frequencies (TOFs) of these RGOs are also calculated, and the P-NRGO has the largest TOF of 58.39. Based on the analysis of synthesis method and catalytic activity, it is proposed that new catalytic sites are generated on P-NRGO. Density functional theory (DFT) calculations also illustrated that the most reactive sites are the structure vacancies with two nitrogen atoms, which is consistent with the results. The conclusion in this study provides new insights into the synergistic effect of N-doping and structural defects of carbon materials and the induced nonradical pathway in advanced oxidation.