The invention provides a method for cultivating bifidobacteria through inulin. The method comprises specific operation steps as follows: cultivation of a stock culture liquid, cultivation of multiple stages of strains and solid culture. A traditional culture medium is changed, inulin is used for cultivation and contains a large amount of synanthrin, and synanthrin can prevent constipation, treat obesity, reduce lingering time of food in stomachs and intestines, increase faeces and effectively treat constipation; synanthrin can improve the viscosity of content and reduce the movement speed of food from the stomach to the intestines, accordingly, the sense of hunger is reduced, the food consumption is reduced, and an anti-obesity effect is performed, inulin is used for cultivating bifidobacteria, bifidobacteria absorbs synanthrin in the cultivation process, so that the activity and the absorption effect of bifidobacteria can be effectively improved, lactic acid and acetic acid can be generated after bifidobacteria are fermented in the intestines of a human body, the utilization rate of calcium, phosphorus and iron can be increased, and absorption of iron and vitamin D is promoted.