Iron is one of the common elements in nature, and it exists two valence states in solution, namely ferric ions and ferric ions. To accurately determine the content of ferrous ions,ferric ions and total iron, this work has explored an improved Ferrozine method. Divalent iron can react with Ferrozine to form a violet complex, which has a maximum absorption peak at 562nm. Using this characteristic divalent iron content can be measured directly. Using hydroxylamine hydrochloride as the reducing agent,ferric iron is reduced to divalent ironit and total iron content can be determined, and further ferric iron content can be calculated. The results show this method can accurately determine free divalent iron and total iron, and the results are consistent to ICP-AES results. Ferric iron content calculated by Ferrozine method is consistent to the result detected by Ferrocyanide method. Moreover,this method can be used to determine iron content of iron oxide nanoparticles dispersed in the aqueous phase. Compared with ICP-AES method, the correction factor is about 85%. So this method is widly applicable,simple,economical and accurate.