The reflectivity and transmittance of ion beam sputtering deposited Cu films of different thickness have been measured by Lambda-900 spectrophotometer. Using Hadley equations, taking into account the correction due to the back surface of the substrate, the optical constants of ion beam sputtering deposited Cu films have been calculated. The results show that the optical constants of Cu films for the same wavelength change evidently along with thickness if the film thickness is less than 100 nm, but reach a certain value if the film thickness is bigger than 100 nm. The relationship between the optical constants of discontinuous Cu films and the wavelength is different from that of continuous Cu films. The relationship between the optical constants of continuous Cu films of different thickness and the wavelength is similar, but the values of the optical constants are different.