The UV photooxidation with Fe(Ⅲ) and H2O2 was employed to treat a naval demsting wastewater, which contains the high COD (chemical oxygen demand) and various metal concentrations exceptionally with high concentrations of citric acid and iron. Because of its iron containment, the Fenton-like reaction automatically took place with the added amount of H2O2. The decomposition rate was found in a sequence of: UV/H2O2/Fe(Ⅲ) > UV/H2O2 > Fe(Ⅱ)/H2O,2. Two H2O2> injection methods, single and multiple points, were evaluated. The multiple-point H2O2 injection was more efficient to decompose the citric acid. The decomposition of the synthetic citric acid and the real derusting citric acid wastewater was also compared. The 93% COD reduction of the derusting wastewater wasachieved using the UV/H2O2/Fe(Ⅲ) treatment.