An environmentally friendly, facile, and economical Fe/N co-doped carbonaceous material (Fe-N@C) was prepared by the in-situ pyrolysis of Fe/N rich Enteromorpha biomass for peroxymonosulfate activation and organic contaminants degradation. Results indicated that Enteromorpha-based catalysts prepared at high pyrolysis temperature displayed some highly graphitic nanosheets with rich nitrogen doped. The graphitic N derived from the intrinsic N in Enteromorpha showed the high correlation with the paracetamol (PCM) removal rate; this was confirmed by the Density Functional Theory (DFT) calculation, showing the high adsorption energy (Delta E-ads -2.62 eV) of PMS molecular adsorbed onto the graphitic N area. A weak correlation between the PCM removal rate and adsorption capacity was also observed, revealing that the PCM catalytic reaction could be greatly accelerated after the pre-adsorption. It was interesting that the intrinsic Fe in Enteromorpha did not affect the PCM degradation, but PCM removal rate of acid treated Fe-N/C was improved as more active sites were formed after the Fe extraction by acid treatment. Both the radical pathways of O-2(center dot)- and non-radical O-1(2) generated in the Fe-N@C/PMS system were the primary mechanisms for the PCM degradation, which was consistent with the Fukui function values of f and f- based on the DFT calculation. In addition, high stability of the carbon-based catalysts was observed after three runs and calcinating regeneration, which showed the promising applications for environmental remediation.