High-performance fluorescence sensors combining convenience, low cost and high sensitivity are prospective for water pollution and human health. Luminescent metal-organic frameworks (LMOFs) as sensors can meet these criteria for high efficient detection of toxic metal ions. Herein, a new LMOF LCU-109 has been fabricated by Sharpless in situ tetrazole synthesis system assisted by polycarboxylic O-donor ligand. It showed a 2D binodal (3,6)-connected kgd structure with multiple N and O dual-functional sites for detecting guest metal ions. As expected, LCU-109 can be highly sensitive and selectively detect trace amounts of Fe 3+ and Cu 2+ ions in an aqueous solution by the luminescence quenching mechanism. Notably, the detection limits (LODs) of Fe 3+ and Cu 2+ ions are 0.0043 and 0.0028 ppm, respectively, in water, which are significantly lower than the minimum standards stipulated for drinking water by the World Health Organization (WHO) (0.3/2.0 ppm) and U.S. Environmental Protection Agency (USEPA) (0.3/1.2 ppm). Moreover, LCU-109 also shows excellent luminescent sensing activities for Fe 3+ and Cu 2+ ions in simulated HEPES biological system and actual river water with low LODs of 0.034/0.019 ppm and 0.0756/0.107 ppm, respectively, which is also lower than the standard of WHO and USEPA. Moreover, convenient and real-time naked eye detection effects are provided by the exquisitely made LCU-109 fluorescent test papers. Importantly, combining density functional theory (DFT) calculations with a variety of experiments, the fluorescence quenching mechanism for energy competitive absorption and weak interaction is further revealed. A 2D MOF displays high performance luminescence quenching for detecting Fe 3+ and Cu 2+ in pure water, actual river water and simulated HEPES with superior low LODs. Multiple experiments and DFT calculations co-verify a weak interaction quenching mechanism.