By taking slot arrays as illustrative examples,the compound structures of Frequency-Selective-Surface(FSS) and dielectric slab were investigated based on modal matching method and experimentation.The frequency responses of FSS structures by different compounding approaches were analyzed,including the influence of polyimide base film and adhesive coating with different thicknesses on resonant frequency.The results show that the influence of base film and adhesive coating in FSS structures can not be neglected,for they have a close relationship with the compounding approach and dielectric thickness.The compound structure should contain adhesive coating to eliminate the effect of air gap.When dielectric constants of base film and adhesive coating are less than or close to that of the slab only,the slab is over 10 times thicker than those of base film and adhesive coating,the influence of base film and adhesive coating on the transmission properties of properly compound structures would be the minimum.The comparison of measurement and computation of frequency response of FSS structures loaded with dielectric slab of a series thickness on one side shows that the flaw of adhesion will change the transmission properties of FSS structures.All factors mentioned above should be considered in FSS design.