In　the　summer　of　2020,　heavy　rains　made　the　Poyang　Lake　region　witnessed　a　big　flood　event.　Remote　sensing　earth　observation　technology　can　help　to　map　and　assess　the　flood　hazard　quickly　and　efficiently.　Therefore,　two　2020　satellite　images　acquired　on　April　15　(Landsat-8　OLI)　and　July　14　(Sentinel-1A　SAR)　were　selected　in　this　study　to　represent　the　dates　before　and　after　the　flood　to　evaluate　the　disaster.　Using　remote　sensing　thematic　information　extraction,　Random　Forest　classification　and　change　detection　technology,　the　inundation　area　and　the　area　of　major　land　cover　types　within　the　inundation　areas　were　revealed.　Associated　with　the　hydrological,　meteorological　and　topographical　data,　the　specific　flooded　sites　and　the　factors　causing　the　disaster　were　identified　and　analyzed.　The　results　show　that　the　flood-inundation　extent　in　the　Poyang　Lake　region　in　2020　is　1961.95　km2,　including　760.54　km2　of　farmland,　71.59　km2　of　forest,　992.02　km2　of　grassland,　26.97　km2　of　soil,　and　110.83　km2　of　built-up　land.　Poyang　County　was　most　severely　affected　in　this　flood　event,　with　a　total　inundated　area　of　514.35　km2.　The　next　two　are　Xinjian　County　with　330　km2　and　Yugan　County　with　310　km2.　The　main　hydro-meteorological　and　topographical　factors　that　caused　the　flood　are　considered　to　be:　(1)　higher　water　level　than　that　in　the　1998　flood;　(2)　failure　of　timely　discharge　of　water　due　to　backflow　of　the　Yangtze　River;　(3)　breach　of　the　embankments.　©　2022,　Science　Press.　All　right　reserved.