Abstract: Ginseng residue discarded by ginseng processing factory was used as raw material and exposed to depolymerization treatment by twin- screw extrusion technique. The effects of water feed rate, extrusion temperature, and particle size of material on the content of soluble dietary fiber (SDF) were investigated by single factor experiments and the process was optimized by response surface test based on single factor experiments. The molecular weight distributions of SDF fraction in unextruded and extruded ginseng residue were determined by gel filtration chromatography. The results showed that the optimum technological parameters of twin-screw extrusion were achieved with 142% of water feed rate, 162℃ of extrusion temperature, 80-mesh of particle size of material, under which the yield of SDF was 24.94%. Molecular weight distributions of SDF fraction in extruded ginseng residue was found to be at 12915 and 5201, which reached the requirement of functional activity of high-quality dietary fiber.