Cathodic　protection　is　usually　used　to　control　the　corrosion　in　service　pipeline.　The　optimum　cathodic　protection　potential　(OCPP)　becomes　a　vital　part　in　order　to　get　the　best　protective　effect　in　the　whole　research　of　cathodic　protection.　Up　to　now,　the　OCPP　is　often　defined　between　200mV　to　300mV　more　electronegative　than　the　free　corrosion　potential　under　usual　circumstance　(neutral　aqueous　solution　or　soil).　However,　the　phenomena　of　over-protection　and　under-protection　usually　occur　in　service　pipeline.　The　cathodic　protection　parameters　of　pipeline　steel　X65,　X80　and　X100　pipeline　steel　in　Dagang　simulated　soil　solution　have　been　investigated　by　using　the　polarization　test　and　AC　electrochemical　impedance　spectroscopy　(EIS)　measurements.　The　values　of　charge　transfer　resistance　(R-t)　by　analyzing　the　EIS　curves　at　various　cathodic　protection　potentials　show　that　the　polarization　resistance　of　the　specimen　has　a　maximum　value　with　negative　shift　of　the　polarization　potential.　The　value　is　negative　to　1000　Omega.cm(2),　hydrogen　evolution　reaction　will　occurs.　The　potentials　of　hydrogen　evolution　of　X65,　X80　and　X100　in　Dagang　simulated　soil　solutions　increase　orderly.　The　study　on　cathodic　protection　parameters　of　X65,　X80　and　X100　pipeline　steels　in　simulated　soil　solution　have　greatly　useful　value　and　practical　significance　on　the　research　about　the　application　of　transportation　pipeline.