The invention provides a preparation method of an infrared transparent window with an electromagnetic shielding function. The window is formed by jointly stacking a sapphire substrate with an oxide film on the sapphire substrate. Two sides of the sapphire substrate are polished; the thickness of the sapphire substrate is 100-10000 microns; the oxide film comprises a stacked layer composed of one or more of tin-doped indium oxide (ITO), aluminum-doped zinc oxide (AZO), gallium-doped zinc oxide (GZO) and fluorine-doped tin oxide (FTO); the total thickness of the oxide film is 0.2-200 microns; the average electron concentration of the oxide film is not higher than 5 multiplied by 10 to the power of 19 cm<-3>. According to the prepared infrared transparent window, the minimum transmittance rate in a wavelength range of 0.78-2.5 microns is 82%, the minimum transmittance rate in a wavelength range of 2.5-5 microns is 53%, the square resistance is less than 100 Ohm/sq, and the shielding efficiency of electromagnetic wave at 1-18GHz is greater than 10dB.