6H-SiC　is　an　important　semiconductor　material.　The　6H-SiC　wafer　is　always　exposed　to　a　high-humidity　environment　and　the　effect　from　the　absorbed　water　molecule　and　some　relative　adsorbates　is　not　negligible.　Here,　the　oxygen　and　water　molecules　absorbed　on　the　6H-SiC(0001)　surface　and　the　dissociation　process　were　studied　with　density　functional　theory.　On　the　6H-SiC(0001)　surface,　absorbed　O-2　is　spontaneously　dissociated　into　O*,　which　is　absorbed　on　a　hollow　site,　and　further　transforms　the　6H-SiC(0001)　surface　into　SiO2.　The　absorbed　H2O　is　spontaneously　broken　into　OH*　and　H*,　which　are　both　absorbed　on　the　top　of　the　Si　atom,　and　OH*　is　further　reversibly　transformed　into　O*　and　H*.　The　H*　could　saturate　the　dangling　Si　bond　and　change　the　absorption　type　of　O*,　which　could　stabilize　the　6H-SiC(0001)　surface　and　prevent　it　from　transforming　into　SiO2.