To　investigate　the　soluble　sugar　change　of　Rrhizoma　Alisma　before　and　after　processing.　Sugars　category　and　contents　were　determined　by　Thin　Layer　Chromatography　(TLC)　and　High　Performance　Liquid　Chromatography　with　Evaporative　Light　Scattering　Detector　(HPLC-ELSD).　The　fresh　Rrhizoma　Alisma　contained　fructose　and　glucose.　The　contents　of　the　two　kinds　reducing　sugar　were　18.15　mg/g　and　15.49　mg/g,　respectively,　comparing　to　14.　11　mg/g　and　8.　58　mg/g　of　the　decoction　pieces　after　processing.　During　the　heat　processing,　the　percentage　of　the　fructose　decreased　22.26%,　while　glucose　decreased　44.61%.　The　liner　range　for　the　two　kinds　sugar　were　from　1　to　12　μg,　and　the　detection　limits　(Signal/Noise=3)　obtained　were　0.12　μg　and　0.16　μg　for　fructose　and　glucose,　respectively.　The　coefficients　of　recovery　of　fructose　and　glucose　were　97.5%　and　99.0%.　The　sharply　drop　of　the　reducing　sugars　indicated　the　happen　of　Maillard　reaction.　©　2018,　Editorial　Office　of　Journal　of　CIFST.　All　right　reserved.