During the preparation of ferric hydroxide with acid leaching filtrate of tailings, schwertmannite is formed because of the formation of a high SO2-4 and high Fe environment with pH values from 2.8 to 3.8 resulting from the gradual dropping of the lye into the filtrate. Schwertmanntie is a metastable mineral, which is transformed into a more stable goethite (iron hydroxide) with the variation of time and system environment. The influence of pH value, temperature and time on the transformation was investigated, and the results show that, under the condition of 60℃, the transformation process in the solution with pH value of 12 for 36 hours can fully convert the schwertmannite into Fe(OH)3.