AlFeCoNiBx high entropy alloy was prepared by vacuum arc melting, and its microstructure and high temperature oxidation behavior were studied. The results show that the increase of B content leads to the transformation of the alloy from "pure B2 phase" to "B2 phase +(FCC1+FCC2)eutectic". After oxidation of AlFeCoNiBx at 900 ℃, With the increase of B content, the thickness of outer CoFe2O4 oxide increases rapidly, while that of inner layer Al2O3 remains unchanged. However, when the content of B exceeds 0.15at%, the continuity of oxide film becomes worse. When the content of B is 0.15at%, the oxidation weight gain is the smallest, the oxide film is well bonded with the alloy substrate, and the oxidation resistance is the best.