The contour shape of the Gaussian moth-eye antireflection microstructure elements is relied on the manufacturing method, the laser interference lithography technology, also effecting its’ reflectivity. This paper gives out the reflectance characteristics of the Gaussian moth-eye antireflection microstructure elements made on the monocrystalline silicon substrate at the mid-infrared with the method of RCWA. We analyzes the different influences on the reflectivity from the cycle, trench depth, wavelength and refractive index by the way of univariate. At last getting the result by MATLAB simulation: the reflectivity become least at the 1.7μm when the cycle between 1~3μm, about 0.05%; the largest reflectivity is about 14%, when the cycle is 1μm. Similarly, the trench depth has great influence on the reflectivity, the reflectance decreased and stabilized with growing of the trench depth. At the same time, the wavelength has influence on the reflectivity. These conclusions is beneficial to designing Gaussian moth-eye antireflection microstructure elements. The conclusion is got that when the angle of incidence different, the azimuth influences the reflectivity.