A concept using sandwiched frequency selective surface(FSS) as a frequency selective reflection plane is proposed for dual-frequency reflectarray system. The reflection phase range of a reflectarray relies on the thickness of the substrate. Usually, we need a tradeoff between the wide phase range and the smooth linear level, especially for dual-frequency system. By inserting an FSS between the reflectarray element layer and the metal ground plane, an additional reflecting plane for the upper frequency band is provided. For lower frequency band, the FSS layer is transparent and the reflecting plane is changed into the real metal ground plane. A 30° scattering angle reflectarray is designed to validate this concept.