In order to achieve the athermalization of conformal optical systms, an infrared imaging system was presented by using the hybrid refractive/diffractive elements made of Si,Ge,and ZnSe and a diffraction surface mounted on the dome’s inner surface.The aberration characteristics of conformal optics and the aberration,thermal and dispersion characteristics of diffractive elements were introduced, then an athermal method by using the thermal compensation characteristics of the diffractive surface on the dome’s inner surface was given.A gimbaled conformal optical system used in mid-IR wavelength was designed.After analyzing the design,it is shown that the conformal optical system makes full use of the charateristics of diffraction elements in good phase compensation,small heat expansion coefficients and big dispersion factors and can work well at -40～70 ℃ while its average MTF value is higher than 0.43 in each Field of Regard (FOR).