The optical constants of Si/Ge multilayers, which prepared by magnetron sputtering system, have been measured by spectroscopic ellipsometry. The measured photo energy range is from 1.5eV to 4.5eV. The effects of sputtering Ar pressure on optical sonstants of Si/Ge multilayers have been analyzed. The results show that the optical constants of Si/Ge multilayers increase with Ar pressure increasing in different degree within lower energy range, but the effects of Ar pressure are no more obvious in higher energy range. The peak positions of the complex dielectric functions and refractive index shift to lower energy direction with Ar pressure increasing. However, the changes of the peak positions of the extinction coefficient are very small, and their values increase with Ar pressure increasing.