The　adsorption　of　H2O　molecule　and　OH　on　UO(100)　surface　has　been　studied　with　periodic　slab　model　by　PW91　approach　of　GGA　within　the　framework　of　density　functional　theory　(DFT).　The　results　of　geometry　optimization　indicate　that　the　adsorption　of　H2O　on　UO(100)　surface　was　chemical.　The　most　stable　structure　of　adsorption　is　that　H2O　aslant　adsorbed　with　the　tilt　angle　is　about　15°,　and　the　corresponding　adsorption　energy　is　predicted　to　be　89　kJ·mol-1.　From　the　calculated　results　of　density　of　states　of　H2O　before　and　after　H2O　adsorption　on　UO(100)　surface,　a　strong　interaction　was　found　between　the　H2O　p　orbital　and　uranium　d　orbital.　Meanwhile,　the　possible　decomposition　mechanism　of　H2O　over　UO(100)　surface　was　discussed.