Electron　paramagnetic　resonance,　in　situ　diffuse　reflection　infrared　Fourier　transform　spectroscopy,　and　temperature-programmed　techniques　by　means　of　the　isotopic　trace　strategies　were　used　to　investigate　the　effects　of　water　vapor　on　oxygen　species,　reaction　pathways,　byproducts　distributions,　and　accumulation　of　the　chlorine　and　carbon　species　on　the　catalyst　surface　for　1,2-dichloroethane　oxidation　over　Ru/WO3　or　Ru/TiO2　catalyst.　The　introduction　of　water　vapor　produced　the　OOH　species　that　were　converted　into　more　active　oxygen　(O-2(-)　and　O-)　species.　The　mulliken　population　analysis　indicates　that　beta　C　and　alpha　C　in　VC　are　bonded　with　H　and　nucleophilic　oxygen　of-OH　in　sequence,　respectively,　which　proved　that　water　directly　promoted　the　transformation　of　vinyl　chloride　to　CH3COOH.　Besides,　water　could　be　partially　adsorbed　at　the　hydroxyl　groups　on　the　Ru/WO3　sample　surface,　which　were　provided　the　adsorption　sites　for　1,2-dichloroethane　molecules.　However,　the　severe　competitive　adsorption　on　the　surface　of　Ru/TiO2　resulted　in　insufficient　oxygen　adsorption　to　supplement　the　oxygen　vacancy.