A　study　on　degradation　of　2,4-dichlorophenol　in　aqueous　solution　using　172nm　excimer　UV　source　is　reported.　Degradation　products　were　analyze　by　Gas　chromatography　time-of-flight　mass　spectrometry.　The　experiment　results　show　that　a　low　concentration　(1　mg/L)　and　a　high　concentration　(10mg/L)　2,4-dichlorophenol　are　directly　irradiated　separately.　By　GC-TOFMS　technique　analysis,　the,　results　indicate　that　under　the　irradiation　the　1mg/L　2,4-dichlorophenol　is　extremely　unstable　and　decompose　completely　in　1.5　minutes.　However,　after　10　minutes　irradiation　on　the　10　mg/L　2,4-dichlorophenol,　the　degradation　products　of　2-chlorophenol,　phenol,　benzenediol　and　benzoquinone　are　detected.　The　possible　process　of　the　degradation　2,4-dichlorophenol　by　excimer　UV　resource　is　presented.