In　order　to　explore　the　three-dimensional　fluorescence　characteristics　of　DOM　during　the　preoxidation　process　of　high　algae-laden　water　with　ClO2,　the　three-dimensional　fluorescence　spectroscopy　technique　was　used　to　qualitatively　investigate　the　changes　of　the　composition　of　intracellular　and　extracellular　organic　matters　in　algae,　and　the　quantitative　analysis　of　changes　in　DOM　composition　was　performed　by　fluorescence　regional　integral　method.　The　results　showed　that　the　IOM　fluorescence　spectrum　of　the　raw　water　containing　high　concentration　of　Microcystis　aeruginosa　had　four　distinct　fluorescence　peaks,　which　were　protein　fluorescence　peaks,　humic　acid　fluorescence　peaks,　fulvic　acid　fluorescence　peaks,　and　soluble　microbial　metabolites　peaks　that　were　represented　mainly　by　tyrosine-like　substances　and　tryptophan-like　proteins　with　14.52%,　48.27%,　16.22%　and　20.99%,　respectively.　While　the　EOM　fluorescence　spectrum　had　only　one　significant　fluorescence　peak　with　63.14%　that　was　mainly　behalf　of　soluble　microbial　metabolites,　and　algae　organics　were　mainly　contained　in　IOM.　The　removal　rate　of　chlorophyll　a　reached　to　73.58%　within　3　minafter　preoxidation　process　with　0.5　mg•L-1　ClO2.　During　this　process,　substances　in　the　regions　,　,　and　represented　by　amino　acids,　proteins,　and　fulvic　acid　respectively　were　released　to　outside　of　the　algal　cell　membrane,　and　then　were　oxidized　to　non-biological　humus　by　ClO2.　Owing　to　algal　cells　burst　constantly,　IOM　was　released　into　the　water　during　the　ClO2　preoxidation　process,　leading　to　the　results　that　the　total　response　value　of　EOM　increased　by　54.89%　within　3　min　and　the　total　response　value　of　IOM　decreased　by　51.50%.　Therefore,　the　drinking　water　treatment　of　high　algae-laden　water　should　pay　close　attention　to　the　release　of　IOM　from　the　algae　cells.　The　appropriate　preoxidation　time　and　dosage　should　be　properly　selected,　and　the　release　of　IOM　should　be　reduced　as　much　as　possible　under　the　premise　of　effective　algae　removal.This　study　will　provide　further　theoretical　and　scientific　basis　for　the　removal　of　algae　by　pre-oxidation　in　drinking　water　and　the　control　of　algae　disinfection　by-products.　©　2019,　Peking　University　Press.　All　right　reserved.