<p>This study combined with the analysis of co-metabolic microbial communities and investigated the enhancing effects of graphene oxide (GO)/iron series (GO/Fe⁰, GO/Fe₃O₄ and GO/Fe₂O₃) on anaerobic treatment of sulfate-laden organic wastewater at varying chemical oxygen demand to sulfate ion (COD/SO₄²⁻) ratios (COD/SO₄²⁻=2.5, COD/SO₄²⁻=1.25 and COD/SO₄²⁻=0.8). Our results indicate that all GO/iron series significantly improved COD_Cr and SO₄²⁻ removal efficiencies and methane production and the enhancement effect was more pronounced at lower COD/SO₄²⁻ ratios. At COD/SO₄²⁻=0.8, compared to the blank control system, the COD_Cr and SO₄²⁻ removal efficiencies and the biogas production rate of the GO/Fe₃O₄ and GO/Fe₂O₃ system were enhanced by 14.1%, 18.3%, and 24.7%; 5.8%, 9.6%, and 23.3% respectively. Notably, with GO/Fe⁰ exhibiting the most significant improvement, the COD_Cr removal efficiency, SO₄²⁻ removal efficiency and biogas production were improved by 34.4%, 41.1% and 42.5%, respectively, relative to the blank control. This mechanism is primarily attributed to the corrosion of Fe⁰ under anaerobic conditions, which releases electrons and H₂ (supplying electron donors for hydrogenotrophic methanogens) and produces elevated levels of soluble Fe²⁺ which precipitates sulfide (reducing H₂S toxicity). Furthermore, they optimized the system’s pH (GO/Fe⁰:7.30–7.69; GO/Fe₃O₄: 7.30–7.57; GO/Fe₂O₃: 7.17–7.54; blank: 6.99–7.18), and oxidation-reduction potential (ORP) (GO/Fe⁰: -350~-370 mV; GO/Fe₃O₄ and GO/Fe₂O₃: -303~-325 mV; blank: -303~-325 mV) and enhanced the physicochemical properties of the activated sludge. Metagenomic sequencing revealed that the addition of GO/iron series maintained the stability of the microbial community structure, thereby conferring stronger shock resistance to the system. This research provides a scientific basis for exploring the application of anaerobic systems in treating sulfate-containing organic wastewater.</p>