Because of material limitations, achieving an athermal design for dual-waveband infrared systems is difficult. This study integrates single-layer diffractive elements to reduce the volume and weight of such a design and introduces optical-digital joint methods to eliminate the impact of low diffraction efficiency. To achieve athermalization, temperature polychromatic integral diffraction efficiency and temperature integral wavelength weight are incorporated in the point spread function (PSF) model. Influence of low diffraction efficiency is eliminated via subsequent algorithm processing. Accordingly, athermal design and processing of a cooled dual-waveband infrared system is achieved and verified via experimental results.