Zinc ash is an industrial raw material for the direct production of zinc oxide, which often contains impurities Fe, Al, Mn and Pb. Flame atomic absorption method and o-phenanthroline visible spectrophotometry were respectively used for detecting iron content in zinc ash. The trace iron in zinc ash was first determined by atomic absorption spectrophotometer. Then Fe3+ was reduced to Fe2+ by reducing agent hydroxylamine hydrochloride. Finally with its determination results as bencehmaik, using o-phenanthroline as complexing reagent and sodium acetate as buffer solution, the content of trace Fe3+ in zinc ash was detected by o-phenanthroline spectrophotometry under a wavelength of 512 nm. The results show when 1 mL of 1.5 g / L o-phenanthroline, 2 mL of 100 g / L hydroxylamine hydrochloride and 5 mL of 1 mol /L sodium acetate solution were added, the chromcgenic reaction could be achieved after 10 min. The method has good color sensitivity and selectivity.