Ciprofloxacin can complex with metal ions by providing carboxyl, carbonyl, and piperazine groups containing N as ligands, thereby affecting its chemical reactions. In this paper, the complexation of ciprofloxacin with common metal ions, the effects of metal complexation and coexistence on chlorination, and the influencing factors have been investigated. The complexation products were characterized by UV absorption spectrum and FTIR, and it was speculated that ciprofloxacin was complexed with metal ions in a ratio of 2:1 in the form of a single dentate ligand or double dentate chelation. The chlorination degradation of ciprofloxacin followed pseudo-first-order reaction kinetics. The reaction rate constants increased by 20% and 160%, the formation of trihalomethane decreased by 11.7% and 36.1%, and the formation of haloacetic acids increased by 12.8% and 19.8% with the coexistence and complexation of Fe³⁺, respectively, compared with the Fe³⁺ absence condition. In the complexation process, electron transport by metal changed the molecular structure and electron cloud density of ciprofloxacin and promoted the formation of strong oxidizing free radicals, resulting in a more obvious effect of ciprofloxacin by metal complexation than by coexistence during chlorination. With different metal complexation, the order of inhibition on trihalomethane formation was Ca²⁺> Mn²⁺> Fe³⁺, and the order of promotion on haloacetic acid formation was Mn²⁺ > Ca²⁺ > Fe³⁺.