Abstract: Objective: Study the optimal extraction technology and the cathartic mechanism of soluble dietary fibers of prunes. Methods: The enzymatic method was adopted to extract SDF from prunes. Single factor experiment and response surface analysis were performed to optimize extracting conditions, and then in vivo test was conducted with the prune SDF. First of all, 7 d loperamide hydrochloride was offered to mice by intragastric administration, a constipation model was built. Prune SDF 14 d was grouped into low dose, medium dose and high dose, and then offered to the mice by intragastric administration. The mice was observed to record following indexes: The weight of the mice, organ coefficients, first black stool excreting time, the number of stool grains excreting in 6 hours, water content in stool, intestinal propulsive rate, gastric emptying rate and the morphological description of gastrointestinal tissue. Results: The optimal conditions for extracting prune SDF were listed as follows: The bath time of mixed prune was 2.9 h. The additive amount of cellulase was 1%. The bath temperature of cellulase was 41 ℃. The bath time of cellulase was 3.8 h, and the yield was 13.238%±0.07% at the moment, and the SDF content was 85.91%±0.46%. After intragastric administration of prunes, there's no obvious impact made on the weight of mice and organ coefficients (P>0.05). The impact on the medium dose group and the high dose group was obvious: The stool excreting time was reduced. The stool grains and water content in stool were increased. The intestinal propulsive rate and gastric emptying rate were raised (P<0.05). The damage to gastrointestinal tissue of mice due to constipation was reduced. The thickness of gastrointestinal tissue was increased (P<0.05). Conclusion: Prune SDF had a function of relaxing bowels for constipation mice, and also could improve the gastrointestinal barrier injury caused by constipation, which played a protective role on the gastrointestinal barrier.