In order to stabilize the optical performance influenced by the temperature changes, an optical seeker with conformal dome on the basis of the passive optical athermallization method is discussed. Reasonable materials are chosen correctly according to athermal equations. The hybrid refractive-diffractive configuration is introduced for the design of athermal optical system design.Ellipsoidal conformal dome could optimize the aerodynamic performance and reduce the heating of the missile dome.missile dome heating. Inverted telephoto triplet is helpful to acquire short focal length and wide FOV. It is shown that an optical system with ±90° unvignetted FOR, F/2, 100% cold stop efficiency was present. A back focal length of 22.8 mm is large enough for the cooled detector, and also MTF are higher than 0.4 at the spatial frequency of 15 lp/mm across the entire field with the working wavelength at 3~5 μm. The specifications can satisfy the requirements of precise seeker, which can ensure the compact design of the system.