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In this work, carbonyl-modified g-C 3 N 4 (CO-C 3 N 4 ) is prepared through one-step calcination of the melamine-oxalic acid aggregates. The visible light-assisted photocatalytic degradation efficiency of the tetracycline hydrochloride (TCH) for CO-C 3 N 4 is significantly enhanced by introducing the peroxymonosulfate (PMS), and the apparent rate constant is greatly increased from 0.01966 min -1 in CO-C 3 N 4 /vis system to 0.07688 min -1 in CO-C 3 N 4 /PMS/vis system. It is found that carbonyl for CO-C 3 N 4 might offer possible reactive sites for PMS activation and collection sites of photo-generated electrons, greatly accelerating carrier's separation for PMS activation. The favorable conditions, such as the higher catalyst dosage, higher PMS amount and alkaline pH, contribute to TCH degradation. The deleterious effects of co-existing anions on the TCH degradation efficiency are ranked in a decline: H 2 PO 4 -  > SO 4 2-  > HCO 3 -  > NO 3 -  > Cl - , and it may be affected by the type and amounts of anions and active radicals generated. The radical trapping tests and electron spin resonance (ESR) detection display that the O 2 - , h + , 1 O 2 , OH and SO 4 - all contribute to TCH degradation. Meanwhile, possible degradation mechanism, intermediates and degradation pathway of TCH are revealed in CO-C 3 N 4 /PMS/vis system. This study will offer a new insight for constructing PMS activation with carbonyl modified g-C 3 N 4 photocatalysis system to achieve effective treatment of organic wastewater., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2020 Elsevier B.V. All rights reserved.)