Corrosion　has　severely　hindered　the　development　and　application　of　high-temperature　hydrothermal　oxidation　technologies　for　disposing　of　chloride-containing　organic　wastewater.　This　study　explored　the　early　corrosion　behaviors　of　316　stainless　steel　(316　SS)　(UNS　S31600),　passivated　by　sodium　phosphate　(Na3PO4)　in　supercritical　water　in　advance,　in　subcritical　water　(at　100,　160,　230,　and　300　degrees　C　and　25　MPa)　having　high　contents　of　oxygen　(O-2)　and　sodium　chloride　(NaCl)　for　50　h.　The　results　show　that　the　corrosion　rate　of　the　phosphate-passivated　316　SS　was　approximately　half　of　that　of　the　passivated　316　SS　(pretreated　in　supercritical　water　without　Na3PO4)　under　the　same　conditions.　The　surface　oxides　of　the　phosphate-passivated　316　SS　consisted　of　Cr2O3,　Fe2O3,　CrPO4,　FePO4,　and　Ni-3(PO4)(2).　The　passivation　pretreatment　of　316　SS　in　supercritical　water　with　Na3PO4　could　form　a　stable　and　protective　oxide　film　containing　phosphates.　These　phosphates　significantly　improved　the　corrosion　resistance　of　316　SS　in　subcritical　water　(containing　oxygen　and　chloride)　by　preventing　corrosive　substances　from　contacting　the　alloy　substrate.