The invention discloses a method for extracting oat beta-glucan, which comprises the following steps: 1) removing starch and floating dust on the surface of oat bran; 2) adding water into the oat bran at 40-50 DEG C, regulating the pH to 7-8, and stirring for 1-5 hours; 3) collecting the filtered liquid after separation, cooling to 10-30 DEG C, regulating the pH to 4.5-5.0, stirring, and then standing for 0.5-3 hours; 4) centrifuging and separating to obtain the filtrate, adding low-temperature alpha-amylase, treating for 1-2 hours under the conditions that the temperature is 35-45 DEG C and the pH value is 5.5-6.5, and filtering with a kieselguhr sheet frame to obtain supernatant liquid; and 5) filtering with a ultrafiltration membrane of which the molecular weight cut-off is 50,000-100,000Da to obtain an oat beta-glucan solution. The organic solvents are not used in the production process of the oat beta-glucan of the invention, operating temperature is not higher than 50 DEG C, and has the advantages of energy saving, environmental protection and high safety. The invention also discovers the application of the oat beta-glucan in improving flushed face and reducing fine wrinkles.