The　iron　Buddha　in　Fuzhou　Kaiyuan　Temple　(Kaiyuan　iron　Buddha)　is　one　of　the　biggest　ancient　ones　existing　at　home　and　abroad.　X-ray　photoelectron　spectroscopy　(XPS)　technique　was　used　to　characterize　the　near　surface　and　near　core　regions　of　the　iron　Buddha.　The　fitting　analysis　of　the　Fe　2p　and　C　1s　spectra　quantitatively　identified　the　existence　of　α-Fe,　Fe3C,　graphite,　α-Fe2O3　and　SiC.　The　results　showed　that　the　corrosion　product　on　the　surface　of　the　iron　Buddha　was　α-Fe2O3,　and　the　near　surface　and　core　regions　of　the　iron　Buddha　exhibited　the　structures　of　white　and　mottled　cast　irons,　respectively,　and　the　SiC　was　brought　from　polishing　agent.　The　respective　graphite　conversion　rate　R,　of　the　cementite　was　obtained　by　calculation,　being　5.45　mol%　and　21.7　mol%,　respectively.　The　authors　discussed　the　characteristics　and　forming　mechanism　of　the　metallographic　microstructure　of　the　iron　Buddha,　unraveled　the　reason　of　the　exceptional　corrosion　resistance,　and　summarized　the　advantages　of　quantitative　analysis　of　the　XPS　on　cast　irons　in　particular　the　historical　iron　relic.　The　analysis　approach　in　this　paper　is　expected　to　be　a　useful　reference　in　the　research　community.　©　2023　Chinese　Mechanical　Engineering　Society.　All　rights　reserved.