The invention discloses an antioxidant absorbent and a preparation method thereof. 85-97 wt.% of carbonyl iron powder with an average particle size of 1-6 [mu]m and 15-3 wt.% of aluminum powder with an average particle size of 20-80 nm are weighed according to a mass fraction to be mixed to obtain carbonyl iron/aluminum mixed powder, and then the carbonyl iron/aluminum mixed powder is subjected toball milling at a speed of 100-250 rpm for 4-8 hours in an argon sealing atmosphere; the mass ratio of the spherical materials is 5-15: 1, so that aluminum powder is uniformly attached to the surfaceof the carbonyl iron powder to prepare carbonyl iron/aluminum mixed powder with an iron/aluminum alloying layer; and then washing and drying are performed with an organic solution, ball milling is carried out at a speed of 250-400 rpm for 8-12 hours, the mass ratio of the ball to the material is 15-25: 1, flaky carbonyl iron/aluminum mixed powder is obtained, the thickness of the flaky carbonyl iron/aluminum mixed powder is less than 1 [mu]m, and then washing, drying and sieving are carried out to obtain the antioxidant absorbent. The problem of low oxidation resistance of existing carbonyl iron powder is solved.