Abstract: The effects of three kinds of bran-rich cereal flour(wheat bran,rye wheat bran and oat bran)on the regulation of intestinal flora were studied by constructing simulated digestion and fermentation system in vitro. The diversity and composition of intestinal flora were analyzed by high throughput sequencing 16S rRNA. The results showed that the α-diversity of gut microbiota was decreased,the composition of intestinal microflora was significantly change,the diversity and the proportion of Bacteroidetes was decreased,the proportion of Firmicutes was increased,and the content of short-chain fatty acids produced by metabolism increased significantly(p<0.05). The effect of oat-rich cereal flour on the proliferation of Bifidobacterium in vitro was significantly higher than the other two groups,which was 1.45 and 2.14 times of wheat-rich cereal flour and rye-rich cereal flour respectively. This study provides a theoretical basis for the preparation of bran-rich cereal flour with good processing performance and high health care value.