The construction of single-atom catalysts (SACs) with high single atom densities, favorable electronic structures and fast mass transfer is highly desired. Here, metal-triazolate (MET) frameworks, a subclass of metal-organic frameworks (MOFs) with high N content, are utilized as precursors since they can enhance the density and regulate the electronic structure of single-atom sites as well as generate abundant mesopores simultaneously. Fe single atoms dispersed in hierarchically porous N-doped carbon matrix with high metal content (2.78 wt.%) and configuration of FeN₄Cl₁ (FeN₄Cl₁/NC) as well as mesopores with proportion of 0.92 (pore-volume ration) were obtained via the pyrolysis of a Zn/Fe-bimetallic MET modified with 4,5-dichloroimidazole. FeN₄Cl₁/NC exhibits excellent oxygen reduction reaction (ORR) activity in both alkaline and acidic electrolyte. Density functional theory calculations confirm Cl can optimize the adsorption free energy of Fe sites to *OH, thereby promoting the ORR process. Further, it demonstrates great potential in zinc-air batteries. This strategy may pave a new way for selecting, designing, and adjusting MOFs as precursors to build high-performance SACs.