Objective To synthesize the oxide films of AlCoCrCu0. 5NiFe high-entropy alloy and characterize their optical properties. Methods The sputtered oxide films of AlCoCrCu0. 5NiFe high-entropy alloy were deposited on the silicon wafer and glass using radio frequency sputter system, and were subsequently annealed. Ellipsometer was employed to analyze thickness, refractive index ( n) and absorption index (k). Results The refractive index n decreased with the oxygen concentration. When the wavelength was 633 nm, n varied between 1. 69 and 2. 40. At the oxygen concentration of 10% , the curve of refractive index had inflection points at the wavelengths of both 475 nm and 600 nm. After 600 nm, n value decreased with the increase of wavelength. At 30% oxygen, the curve of refractive index had inflection points at 500 nm and 600 nm. After that, the change of n value was minor. At 50% ox-ygen, there was an inflection point on the refractive-index curve at the wavelength of 525 nm. After that, n value increased with the increase of wavelength. The absorption index of AlCoCrCu0. 5 FeNi oxide film increased with the increase of oxygen concentration in the wavelength of between 450 nm and 550 nm. k value changed less obviously between 550 nm and 850 nm wavelengths. The film color became deeper with the increase of oxygen concentration. After the film was annealed at different temperatures, the film color became even deeper. The film thickness decreased with the increase of the oxygen concentration. Conclusion Decreasing oxygen concentration resulted in oxide films of AlCoCrCu0. 5 NiFe high-entropy alloy with high refractive index. There was an inflection point in the absorption index curves of different oxygen concentrations. With oxygen concentration increasing, the wavelength value of the inflection point decreased, the film thickness increased, and the film color became deeper.