As an important part of metamaterials, the dielectric layer is one of the key factors influencing the properties of metamaterials. When the size and surface metal-pattern of metamaterials had been fixed, control rules related to the permittivity and thickness of dielectric layer were analyzed within terahertz band. For the first time, the formula related with the frequency and permittivity was defined in this article. The results show that, with other parameters kept constant, the frequency response of metamaterials mainly depends on the real part of permittivity, while the absorption mainly depends on the thickness of the dielectric layer. According to the conclusions, we further proposed a new method for designing the metamaterials: firstly, putting the required response frequency into the deduced frequency equation and calculating the permittivity, by which suitable dielectric material in accordance with the calculation can be chosen; secondly, under the chosen frequency, the highest or desirable terahertz absorption can be obtained by adjusting the thickness of the dielectric layer. This design method can effectively predict and control the response properties of the metamaterials just by changing the parameters of the dielectric layer. Importantly, our method not only can obviously shorten the design cycle, but can also greatly reduce the difficulty in designing the metamaterials.