A kind of frequency selective surface (FSS) with a new periodic pattern has been designed by using the pattern obtained by rotating the thirdorder straight cross branch patch into 45° as a basic periodic unit. The dualband frequency selective composite material has been prepared with compounding of FSS and the polymethyl acrylamide foam. The electromagnetic wave insertion loss in the range of 1 GHz to 18 GHz has been studied by designing the frequency selection surface size and foam thickness. The results show that the experimental value and the simulation value of the electromagnetic wave insertion loss of this dualband frequency selective composite material in a specific frequency range are almost the same when the thickness of FSS is 12 μm, the boundary width is 30 μm and the thickness of foam on both sides is 5 mm. That is, the insertion losses of frequency points of 90% are all less than 0.9 dB in the range of 2.5~3.5 GHz and 8.5~11 GHz. As the incident angle of the electromagnetic wave offsets, and the inband insert loss increases, the effective bandwidth reduces.