The construction of double active sites for pollutant adsorption and peroxymonosulfate (PMS) activation on the surface of catalyst is conducive to further enhancing the pollutant-removing effect. Herein, a N,O co-doped carbon-encapsulated tricobalt tetraoxide (Co3O4@N,O–C) with double active sites is prepared by a one-step laser carbonization method. The optimized Co3O4@N,O–C shows excellent tetracycline (TC) removal ability, in which the k value reaches 0.608 min−1. On the surface of Co3O4@N,O–C, TC is adsorbed to the N site, and PMS is activated at the O site. Building double active sites on the catalyst surface not only avoids competition for the active site, but also confines the pollutant molecules to the surface of the catalyst, thus shortening the migration distance between reactive oxygen species (ROS) and the pollutant and boosting the removal efficiency of pollutants. In addition, the Co3O4@N,O–C/PMS system exhibits both good resistance to environmental interference and cyclic stability. Finally, a practical continuous flow reactor based on Co3O4@N,O–C catalyst is built, which shows a stable and efficient TC degradation performance.