This study investigates the Hydroxylamine (HAm)-driven Cu(II)/peroxymonosulfate (PMS) system, known for promoting toxic nitro(so)phenols formation during phenol degradation. It focuses on the intricate factors affecting nitro(so)phenols formation, aiming to unravel the complex mechanisms in the transformation of phenol to nitro(so)phenols within the HAm-Cu(II)/PMS system. Findings reveal that reaction conditions significantly impact the formation of nitro(so)phenols by affecting the phenol degradation intermediate (PhO•) and HAm oxidation reactive nitrogen species (•NO, •NO2). Additionally, the levels of specific reactants and coexisting compounds also affect the pathway of nitro(so)phenols formation. At high concentrations of HAm and halogen, the •NO and halogen radicals generated may directly oxidize phenol to produce PhO•, which in turn reacts with •NO and •NO2, and thus establishing a different nitro(so)phenols formation path from that dominated by SO4∙-. The oxidation products and driving factors of HAm vary at different stages, affecting the production of nitro(so)phenols. Moreover, the presence of halogen and natural organic matter (NOM) alters the formation of nitro(so)phenols under real water conditions compared to pure water. Overall, the investigation into various influencing factors indicates that advanced oxidation process enhanced by hydroxylamine, not just limited to persulfate-related reactions, has the potential to produce nitro(so)phenols when treating phenol-containing water.