The invention relates to a polysaccharide quantitative detection method and system. In this method, polysaccharide is separated by chromatographic column, hydrolyzed and then reacted with fluorescent derivatization reagent, and the content of polysaccharide is obtained by measuring the generated fluorescent derivatives with fluorescence detector. The system for polysaccharide detection of the invention sequentially comprises a high performance liquid chromatography column, a hydrolysis reactor, a fluorescence derivatization reactor, a cooling tube, a fluorescence detector and a workstation or a recording device. The detection system of that invention greatly improve the detection sensitivity by hydrolyzing polysaccharide first and then react with fluorescent derivatization reagent, and is suitable for quantitative detection of various types of polysaccharide content, and the detection limit can reach tens of ng.