The corrosion behavior of titanium alloy Ti6Al4V in 44.6 wt% sulfuric acid solutions, was studied via potentiodynamic polarization, electrochemical impedance spectroscopy (EIS), Mott–Schottky and X-ray photoelectron spectroscopy (XPS) techniques. The results indicated that the Fe3+ played an important role in the passivation and stability of the passive film formed on Ti6Al4V. When the concentration of Fe3+ reached to 0.001 M, the hydrogen evolution reaction (cathodic process) was remarkably influenced, the anode process of the corrosion reaction changed from active state to passivation state, and it showed an enormous increase of the impedance values (Rc) with the capacitive arc varying from two to one. XPS results showed that as the concentration of Fe3+ increased, there were less intermediate valence oxides Ti2O3 and more stable valence oxides TiO2. Fe3+ made more intermediate valence titanium ions or instability titanium oxides transformed into stable valence oxides, which enhanced the stability of the passive film.