[Objective] This study aimed to efficiently utilize the resources of Phlebopus portentosus and develop its polysaccharide functional food. [Methods] The mycelium of P. portentosus was cultured and fermented, and the combined fermentation broth was concentrated at low a temperature and reduced pressure. Then, precipitated by ethanol, separated, purified by DEAE-52 cellulose column chromatography, and the polysaccharide was finally refined by dialysis to remove the small molecular impurities. The total sugar content was determined by phenol-sulfuric acid colorimetry, the monosaccharide composition was determined by liquid chromatography-mass spectrometry (LC-MS), and the impurities such as nucleic acid and protein were detected by ultraviolet spectrophotometer. The structure of polysaccharides was analyzed preliminarily by infrared spectroscopy (IR) and nuclear magnetic resonance spectroscopy (NMR). [Results] The content of total sugar was 84%. The main monosaccharides of the polysaccharide were glucose, mannose, galactose, and arabinose, the molar ratio of which was 2.07∶1.95∶1.00∶1.58. Obvious polysaccharide absorption peaks were shown in the infrared spectrum and nuclear magnetic resonance spectra, through which an α-type pyranose can be inferred in the polysaccharide. [Conclusion] The polysaccharides prepared from the fermentation broth of P. portentosus were mainly composed of four monosaccharides, the structure of which contained α-pyranose.