Abstract: Liquid atomization is widely used in industry, agriculture and other fields. During the atomization process, the liquid first forms a liquid film, and the liquid film becomes unstable in the gas-liquid boundary layer, resulting in the liquid film being broken. Therefore, the instability of the liquid film plays a very important role in the liquid atomization, and it is necessary to study the instability of the liquid film. In this paper, the instability of viscous planar liquid film in compressible gas was studied by numerical calculation method. Firstly, the velocity distributions of viscous planar liquid film and gas were derived, based on which the instability of viscous planar liquid film was investigated by spectral methods. It is found that in the sinuous and varicose modes, applying an electric field will accelerate the breakup of the plane liquid film. The sinuous mode is more unstable than the varicose mode, indicating that the sinuous mode plays a leading role in the instability of the plane liquid film. Increases of gas Mach number, electrical Euler number, gas Reynolds number, Weber number and momentum flux ratio accelerate the breakup of the liquid film. With the increase of the thickness ratio of gas boundary layer to liquid film and the liquid Reynolds number, the growth rate of the disturbance wave decreases, and the liquid film becomes more stable.