Abstract: The formula of reflectivity of single-layer loss materials was presented at the oblique incidence of electromagnetic wave. Using the three-dimensional mesh method, the influence factors on the reflectivity was discussed, such as the incidence angle, the material electromagnetic parameters, the thickness of the material and other factors. At the same time, a computer-aided design for a given electromagnetic parameters of single layer structure was performed. The optimization results showed that the theoretical study will play a directional role for the design and application of experimental materials.