This article was aimed to study the effect of soluble dietary fiber in sweet potato residue on intestinal flora by vitro fermentation. Soluble dietary fiber was extracted from sweet potato residue by using enzyme hydrolysis. Then it was used as the main carbon source of vitro cultivation of intestinal flora and to observe the pH change， gas production rate， the content of NH3-N of the fermentation liquor after 0， 6， 12 and 24 h. Short chain fatty acids （SCFA） of the fermented liquid at 12， 24， 48 h were analyzed respectively. The effects of soluble dietary fiber on intestinal flora was determined through the changes of the above indicators. Compared with the control group， results showed that the experiment group added soluble dietary fiber could significantly reduce（P＜0.05） the pH of fermentation liquid， decrease the content of NH3-N in fermentation liquid， and significantly increase（P＜0.05） the output of SCFA which proved that soluble dietary fiber in sweet potato residues could improve the metabolites of intestinal flora and contribute to human intestinal health.