Taking Flammulina velutipes powder as the main raw material， the single-screw extrusion modification process was used to prepare high-quality Flammulina velutipes dietary fiber. The water holding capacity， oil holding capacity， swelling force， combined hydraulic power， cholesterol adsorption capacity， and the ability to combine sodium glycylcholate and sodium taurocholate of Flammulina velutipes dietary fiber were compared. The structure of dietary fiber of Flammulina velutipes before and after modification was studied by electron microscope， Fourier infrared spectroscopy， and X-ray diffraction scanning. The results showed that the soluble dietary fiber of high-quality Flammulina velutipes dietary fiber increased compared to ordinary Flammulina velutipes dietary fiber， reaching （10.210±0.130）%. When the particle size of high-quality Flammulina velutipes dietary fiber was 100 mesh， the water holding capacity was （16.115±0.120） g/g， the oil holding capacity was （6.201±0.060） g/g， the swelling force was （16.958±0.120） mL/g， and the combined hydraulic power was （8.044 ±0.090） g/g， which was significantly improved compared with ordinary dietary fiber. At pH=2.0 and pH=7.0， the cholesterol adsorption capacity of high-quality Flammulina velutipes dietary fiber could reach to （0.359±0.004） mg/（mL·g） and （1.107±0.004） mg/（mL·g）， respectively. When the particle size of high-quality Flammulina velutipes dietary fiber was 120 mesh， the ability to combine sodium glycylcholate and sodium taurocholate was better， reaching （67.367±0.600）% and （63.149±0.400）%， respectively. Scanning electron microscopy results showed that the surface of the high-quality Flammulina velutipes dietary fiber after extrusion modification was loose and porous. Fourier transform infrared spectroscopy analysis showed that the structure of main functional groups did not change significantly before and after modification， and the intensity of some characteristic peaks weakened after modification. X-ray diffraction scanning analysis showed that the crystal structure of Flammulina velutipes dietary cellulose did not change， and the diffraction intensity weakened. The extrusion-modified high-quality Flammulina velutipes dietary fiber improved its physical and chemical functional properties and changed its microstructure.