Abstract: The analysis on polarization curve and electrochemical impedance spectroscopy(ESI) of Ti6321 and TC4 ELI alloy in the artificial seawater solution with PH=7 and PH=1.5 has been carried out. It is found out that the non-integrative oxide of Ti element participates in the process of anode polarization, and that the hydrogen electrochemical evolution in negative polarization process is controlled by H+ concentration and desorption, and has different Tafel slopes. Ti6321 and TC4 ELI have stable passive film in the neutral artificial seawater, while in the acid environment, the passive film on the surface of TC4 ELI isn't stable, and the polarization resistance R_p<0 appears in the impedance spectrum.