The effect of different oil-based diets on the blood index and the gut microbiota of rats was investigated. Rats in sample treatment groups were fed with stewed lard, refined lard, fish oil and soybean oil at a normal dose of 16.9% for 6 weeks. Compared with refined lard group, stewed lard treatment group showed reduced fasting blood sugar and blood lipid levels and improved nutrient absorption capacity of the intestine. The blood indexes of glucose (Glu), total cholesterol (TC) and total triglyceride (TG) in fish oil treatment group were relatively low. The abundance of Bacteroidetes in the fat-free group decreased, and the abundance of Firmicutes increased. The Firmicutes/Bacteroidetes ratio of the fish oil group was relatively low, and the Firmicutes/Bacteroidetes ratio of the stewed lard group and the soybean oil group was lower than that of the refined lard group. The abundance of Bacteroidaceae in the stewed pork fat group was increased. Research results show that fat-free diets will increase the risk of obesity to a certain extent; compared with refined lard, stewed lard, soybean oil and fish oil can reduce the risk of obesity to a certain extent; the addition and types of dietary fat will affect the abundance and diversity of rat intestinal flora.