Based　on　three-dimensional　fluorescence　spectroscopy　and　ultraviolet　visible　spectroscopy,　the　composition,　source　and　structural　characteristics　of　dissolved　organic　matter　(DOM)　in　the　overlying　water　of　Tongzhou　area　of　Beiyun　River　in　flood　and　non-flood　season　were　compared　and　analyzed,　and　the　relationship　between　the　content　of　N　and　P　in　the　overlying　water　and　the　composition　of　DOM　was　established,　The　results　indicated　that　the　DOM　content　in　the　overlying　water　of　Tongzhou　area　ranged　from　9.17mg/L　to　27.78mg/L,　showing　a　general　trend　of　non-flood　season　＞　flood　season,　upstream　＞　downstream.　The　temporal　and　spatial　characteristics　of　DOM　content　were　significantly　different.　The　molecular　weight　of　DOM　in　flood　season　was　smaller　than　that　in　non-flood　season,　and　the　aromatic　degree　of　DOM　in　flood　season　was　lower　than　that　in　non-flood　season;　the　value　of　DOM　A253/A203　in　flood　season　was　higher　than　that　in　non-flood　season.　DOM　in　flood　season　was　affected　by　both　land-based　humus　and　biological　sources,　while　that　in　non-flood　season　was　mainly　affected　by　microbial　activities.　The　concentrations　of　protein　and　humus　in　flood　season　were　significantly　lower　than　those　in　non-flood　season.　Protein　components　accounted　for　more　in　non-flood　season,　while　humus　components　accounted　for　more　in　flood　season.　The　maximum　fluorescence　intensity　of　C1,　C3　and　C4　in　DOM　could　indirectly　reflect　the　potential　risk　of　eutrophication　in　Beiyun　River.　©　2021,　Editorial　Board　of　China　Environmental　Science.　All　right　reserved.