Ultra　-high　performance　concrete　(UHPC)　is　an　innovative　cement　-based　composite　material　characterized　by　extremely　high　durability　and　mechanical　properties,　which　provides　a　potential　possibility　of　using　non　-desalted　sea　-sand　as　aggregate.　However,　the　long-term　steel　corrosion　behavior　in　UHPC　prepared　by　simulated　sea　-sand　under　different　immersion　environments　remains　unclear,　which　is　of　great　significance　for　the　application　of　sea　-sand　UHPC　in　practical　engineering.　In　this　study,　the　pore　structure　of　sea　-sand　UHPC　matrix　was　measured　using　nitrogen　adsorption/desorption　method.　The　corrosion　behavior　of　rebar　in　sea　-sand　UHPC　with　different　endogenous　chloride　ion　contents　soaking　in　pure　water　and　NaCl　solution　was　characterized　by　linear　polarization　resistance　(LPR),　electrochemical　impedance　spectroscopy　(EIS)　and　cyclic　polarization　(CP).　The　experimental　results　show　that　the　initial　UHPC　pore　structure　is　refined　by　incorporation　of　sea　-sand,　and　is　similar　to　that　of　ordinary　UHPC　at　the　later　hydration.　Regardless　of　the　endogenous　chloride　ion　content　and　immersion　environment,　the　corrosion　rate　evaluated　by　corrosion　current　density　(icorr)　and　polarization　resistance　(Rp)　of　reinforcement　in　UHPC　is　extremely　low.　The　measurement　of　EIS　shows　that　UHPC　group　has　higher　matrix　resistance　(Rc)　and　charge　transfer　resistance　(Rct),　while　lower　electric　double　layer　capacitance　(CPEdl)　of　reinforcement,　which　indicates　that　the　steel　in　UHPC　made　of　sea　-sand　is　still　in　a　state　of　passivation.　However,　the　steel　bar　in　comparison　specimen　OPC　soaking　in　NaCl　solution　is　in　the　corrosion　stage.　Furthermore,　sea　-sand　UHPC　possesses　of　excellent　ability　of　anti　-pitting　corrosion　of　reinforcement　after　180　days　of　immersion　in　NaCl　solution.