Effects of four types of cereal dietary fibers (DF) on blood glucose, inflammatory factors and gut microbiota in db/db mice were investigated. The db/db mice were fed with diets containing four types of dietary fibers of wheat (WDF), brown rice (BDF), oat (ODF) and buckwheat (BWDF) respectively. The fasting blood glucose (FBG) level was measured every two weeks, and oral glucose tolerance tests (OGTT) were conducted at the 8th and 14th weeks. At 14 weeks, feces were collected to analyze the changes of microbiota, and serum was collected to determine the level of blood lipid and inflammatory factors. Four types of cereal DF could reduce the FBG and the area under the blood glucose curve (AUC) at 8 weeks in db/db mice, improve dyslipidemia and reduce the concentration of blood pro-inflammatory factors (P < 0.05). All four types of cereal DF could increase the diversity of gut microbiota and change the abundance of different microbiota. Among them, WDF mainly increased the abundance of Faecalibaculum and Romboutsia, BDF increased the abundance of Actinobacteriota and the ratio of Firmicutes to Bacteroidota (F/B), ODF mainly promoted the proliferation of Alistipes, and BWDF increased the abundance of norank_f__Muribaculaceae and decreased the level of Bacteroides. Correlation analysis showed that F/B and Actinobacteriota were significantly negatively correlated with FBG, AUC, pro-inflammatory factor (IL-8) and low-density lipoprotein cholesterol (LDL-C) levels, and positively correlated with anti-inflammatory factor (IL-10) and high-density lipoprotein cholesterol (HDL-C) levels, while Bacteroides was the opposite. Alistipes, Faecalibaculum, and Romboutsia were negatively correlated with pro-inflammatory factors IL-1β, IL-8 and TNF-α respectively. Four types of cereal DF can improve the glycolipid metabolism disorder and inflammatory response in type 2 diabetic db/db mice by increasing the diversity of gut microbiota and exerting different regulatory effects on microbiota.