The design and fabrication of metallic mesh based on germanium substrate were investigated to satisfy the electromagnetic shielding requirements of germanium optical windows. Through theoretical analysis of the effect of metallic mesh structure on optical transmittance and electromagnetic shielding effectiveness, CST software simulates the effect of metallic mesh period, thickness, and substrate resistivity on electromagnetic shielding. According to the simulation results, appropriate parameters are selected for fabricating the mesh microstructure. The mesh structure that meets the requirements was fabricated using laser direct writing lithography. The metallic mesh microstructure has a 400μm period and a 12μm line width. The average transmittance of 8-12μm band measured by infrared spectrometer is 87.1%. The lowest electromagnetic shielding effectiveness exceeds 28.1dB, while the average electromagnetic shielding effectiveness of the 240MHz to 18GHz range assessed by the vector network analyzer is 34.4 dB. This paper describes the simulation and fabrication of metallic mesh microstructures on germanium substrates. These microstructures have excellent optical and electrical properties, which is crucial for fabricating optical windows with high optical transmittance and potent electromagnetic shielding.