90° or 270° phase retarder is introduced to change the polarization of light from linear to circular. The combination of metal and dielectric is used in this design. The silver thin film with excellent optical quality is used as the metal layer. 270°±1°phase shift between p- and s-polarization component as well as broadband high reflection mutilayer coatings is designed by optimizing dielectric layers in the wavelength range 1000 ~ 1100 nm at 45°. The errors produced in manufacturing and using process are also analysed. Under the manufacturing precision nowadays, more attention ought to be paid to ensure that the phase shift error δ<7.2°and reflectivity over 99.9% are achieved in the 1000~1100 nm spectral region for use at 45°。