Abstract: 1-phenyl-3- methyl-5- pyrazolone ( PMP) was applied to derivate polysaccharide degradation product.Then liquid chromatography with ultraviolet detector- high resolution quadrupole tandem time of flight mass spectrometry ( HPLC- UV- Q- TOF- MS) was used to detect and analyze monosaccharide compositions and enzymatic hydrolysate of Ganoderma atrum polysaccharide. The results showed that the monosaccharide compositions of Ganoderma atrum polysaccharides were mainly glucose, mannose, galactose. The degradation products of β-glucanase were monosaccharides and oligosaccharides from disaccharide to pentasaccharides, but Ganoderma atrum polysaccharides were mainly degraded into monosaccharides by pectic enzyme.