Pt 1-x Mn x /Co multilayers were prepared by magnetron sputtering method. The crystal structrue was analysed by large and small angle X ray diffraction. The ralationship between structure and magneto optical properties in PtMn/Co multilayers was studied. Through measurement and analyses, the Kerr spectrum, Kerr ellipticity spectrum and Kerr loop shown the changing rules with the increase of doped Mn concentration. The physics mechanisms are discussed.