Singlet oxygen (O) is a thrilling active species for selectively oxidating organic substances. However, the efficient and selective generation of O maintains a great challenge. Here, we develop a donor-acceptor structured g-CN by covalently engineering benzenetricarboxaldehyde (BTA) onto the fringe of g-CN. The g-CN-BTA exerts high-efficiency O generation with nearly 100% selectivity via peroxymonosulfate (PMS) photocatalytic activation upon visible light illumination, exhibiting obviously boosted efficiency for selective elimination of atrazine (ATZ). The consequences of experiments and theoretical calculations demonstrate that BTA units serve as electron-withdrawing sites to trap photogenerated electrons and facilitate the adsorption of PMS on the electron-deficient heptazine rings of g-CN. As such, PMS can be in-situ oxidated by the photogenerated holes to selectively produce O. Besides, the g-CN-BTA/PMS system delivers high stability and strong resistance to the coexisting organic ions and natural organic matter, demonstrating great potential for selectively removing targeted organic contaminants with high efficiency.