Ultra-high　performance　concrete　(UHPC)　is　typically　defined　as　an　advanced　cementitious　material　which　exhibits　excellent　mechanical　property　and　superior　durability.　The　development　of　UHPC　made　with　sea-sand　addresses　the　challenges　associated　with　the　shortage　of　river　sand　in　producing　concrete　for　a　marine　construction.　In　this　study,　UHPC　matrix　was　prepared　by　using　simulated　sea　sand　with　different　levels　of　chloride　and　mineral　admixtures　included　fly　ash　and　slag.　The　passivation　behavior　of　steel　bars　embedded　in　sea-sand　UHPC　specimens　were　investigated　by　electrochemical　workstation.　In　addition,　the　microstructure　of　sea-sand　UHPC　matrix　was　characterized　by　rapid　chloride　test,　alkalinity　test　and　SEM-EDS.　The　experimental　results　showed　that　in　the　early　age,　the　alkalinity　of　sea-sand　UHPC　matrix　increases　with　the　increment　of　endogenous　chloride　ion,　and　the　introduction　of　fly　ash　in　the　matrix　has　higher　alkalinity　than　slag.　The　corrosion　current　density　icorr　of　steel　bar　in　sea-sand　UHPC　gradually　decreases　with　the　age,　and　essentially　being　lower　than　0.1　mu　A/cm2.　Due　to　the　pozzolanic　effect,　the　utilization　of　fly　ash　and　slag　prolongs　the　stabilization　age　of　icorr　evolution.　The　reinforcement　embedded　is　able　to　be　in　the　stable　passive　state　regardless　of　the　endogenous　chloride　ion　content.　The　incorporation　of　fly　ash　and　slag　has　little　effect　on　the　densification　of　passivation　film.　Compared　to　the　endogenous　chloride　ion　level,　the　alkalinity　of　matrix　has　a　more　significant　effect　on　the　growth　of　the　charge　transfer　resistance　of　steel　bars　in　sea-sand　UHPC,　which　is　associated　with　the　denser　passive　film　and　built-up　of　Ca(OH)2　layer　near　the　steel　bars.