The effects of structure parameters of substrate on the frequency response characteristics of combination element frequency selective surface (FSS) which assembles Y element and circular aperture element are studied using the spectral domain method. Frequency response characteristics of the combination element FSS show double-band characteristic including band pass and band stop. Arm-length of Y element has a very important effect on FSS frequency response characteristic, compared with other parameters. When the arm-length is increased from 2.0 mm to 3.5 mm, the resonant frequency of band pass is drifted by 4.2 GHz and the resonant frequency of band stop is drifted by 7.0 GHz to low frequency, the transmission bandwidth of band pass is decreases by 6.6 GHz and the bandwidth of band stop increases by 4.4 GHz at -5 dB.