Objective To investigate the effects of steam explosion pretreatment on the microstructure of oats, the content of β-glucan, the digestion characteristics of starch, and its effect on obesity in mice fed a high-fat diet.Methods The effects of steam explosion treatment under different pressures (0.3, 0.5 MPa) and time (30, 60, 90 s) on the microstructure of oats and the composition of β-glucan are investigated, and the obesity inhibitory effect of steam-exploded oats in a simulated high-fat diet environment is studied.Results Steam explosion can destroy the ordered structure of the oat cell wall, increase the content of slowly digestible starch, the content and dissolution rate of water-soluble β-glucan, and reduce the content of resistant starch. It is positively correlated with the intensity of the steam explosion. At 0.5 MPa, the content and dissolution rate of water-soluble β-glucan are the highest. The intervention of steam-exploded oats in mice fed a high-fat diet can reduce the body weight gain of these mice. Compared with the high-fat diet group, the highest reduction in body weight can reach 10.5%, and it can also reduce fat deposition in the liver.Conclusion Steam explosion can optimize the microstructure of oats, increase the content of water-soluble β-glucan, improve the digestion characteristics of starch, and significantly inhibit obesity in mice induced by a high-fat diet.