To establish a quantitative method for the content determination and monosaccharide composition analysis of Konjac glucomannan (KGM) in Konjac refined powder by pre-column derivatization high performance liquid chromatographic method (HPLC).The two derivatives combined reducing monosaccharides with 1-phenyl-3-methyl-5-pyrazolone (PMP) were separated by reverse-phase HPLC using a developed fragment gradient elution process, and monitored by ultraviolet detector at 250 nm. The broad reagent peak of PMP was separated very well from all the PMP-sugars, and good separation was achieved for derivatives of mannose and glucose. The quantitative methods of two reducing monosaccharides were studied by the method combined internal and external standard; while the KGM content in Konjac refined powder was determined.Linearity of glucose was good (r = 0.9990) in range of 1.002-8.016 nmol; while mannose (r = 0.9994) in range of 1.001-8.008 nmol. The average recovery of this method was 98.1%, RSD of repeatability was 1.72%. KGM content in Konjac refined powder was 79.5%, ratio of glucose to mannose in KGM was 1:1.51.This method is a sample, convenient and rapid method that can determine KGM content and analyze monosaccharide compositions in KGM, which will be helpful to quality assessment of Konjac refined powder.