With the rapid development of infrared temperature measurement technology, infrared thermometer plays an important role in both military and civil fields, so it calls for higher measurement accuracy. It should be observed that a couple of years have witnessed an increasing number of people who are concerned that radiation source consisting of area blackbody is the vital device to calibrate the non-contact thermometer. Spectral emissivity is an essential parameter to describe the performance of radiation sources, while there is less research involved in the effect of blackbody surface topography on emissivity. It is manifested that the emissivity of the area blackbody is related to the combination structure of the evagination cone and coating. In order to design a remarkable performance area blackbody with high emissivity, the paper takes the area blackbody with convex cone structure as the basic model, adding components of spacing resembling grating and coating, and establishes an area blackbody model with different structural parameters, cell spacing and coating thickness. Graphite and silicon nitride is set as the base material and the coating material, respectively. Reflectivity is obtained by measuring the variation of reflected radiation with related soft. Then the emissivity is calculated through the relationship between reflectivity and emissivity, drawing the curve of spectral emissivity in the range of 3~14 μm. According to the electric field distribution of the surface and curve of spectral emissivity, we analyze the influence of parameters such as the ratio of width to length, coating thickness and spacing on emissivity. It is shown that the height of the structure unit is proportional to spectral emissivity, and emissivity is optimized due to narrower width, which increases as the ratio of width to length decreases. The dropping trend of spectral emissivity is changed by the coating structure in which the emissivity increased at the wavelength above 11 μm, and the emissivity rise with the increasing coating thickness. What’s more, the spacing structure is proportional to emissivity. The height and width of the unit structure of the original area blackbody are set at 10 and 1 μm, respectively. A coating with a thickness of 2 μm and a spacing structure with a width of 2 μm are sequentially added to the original model for simulation calculation. The optimized blackbody radiation source has advantages in the long wavelength band, and the spectral emissivity with a minimum value of 0.966 is stable in the range of 3~14 μm. The electric field distribution shows the influence of these structural factors on the surface energy of the area blackbody, and the optimized model parameters can be used to manufacture a realistic area blackbody. Simulation results illustrate that a smaller aspect ratio, thicker coating and larger spacing improve spectral emissivity, which provide a theoretical reference for the manufacture of radiation sources consisting of area blackbody with high radiation performance.