With the increasing demand of infrared imaging technology for time resolution, spatial resolution, spectral resolution and optical stability, the contradiction between the four is becoming more intense. The molecular filter was a filter device with a comb-like discrete transmission spectrum type. The selective transmission was realized by the resolution of the wavelength of the light by the molecular energy level transition. The effect was "optical" but the mechanism was "quantum". Molecular filtering provided a new way for conflict resolution. Based on the theory of molecular spectroscopy, the working mechanism and theoretical model of three types of molecular filter imaging techniques, such as differential absorption, magneto-optical rotation and Doppler modulation, were presented. Combined with the related work of the research team, the applications were introduced separately: differential absorption molecular filtering in remote sensing monitoring of vehicle exhaust, magneto-optical rotation molecular filtering in combustion diagnosis, and Doppler modulated molecular filtering in spaceborne atmospheric wind and temperature remote sensing. Finally, the technical characteristics and applicability of the three mechanism filtering methods were analyzed.