Sandwiched frequency selective surface (FSS) is proposed as an additional reflection surface for a dual-frequency reflectarray system. The range of reflection phase for a reflectarray depends on the substrate thickness sensitively. Usually, a tradeoff between the smooth linear level and the wide reflection phase range is needed, especially for a dual-frequency system. By inserting an FSS between the ground plane and the reflecting element layer, a selective plane for the dual-frequency band is provided. For the higher frequency band, the FSS layer is a reflection plane. For the lower frequency band, it is transparent and the reflection plane is changed into the metal ground plane. A dual-band reflectarray with a scattering angle of 30 degrees is simulated and measured to validate this concept.