Abstract: A method of athermal infrared telephoto objective was introduced in this paper. Telephoto lens model was combined with athermal model to find out and unify the relationship of focal power distribution. First, distribute the optical power of the fore group and the rear group on the basis of the principle of telephoto objective, choose the reasonable solution of the optical power of the two groups; then choose the appropriate material and distribute the optical power within each group to realize the ability of athermalization, finally computer-aided software was used to correct aberration. In order to prove the feasibility of the scheme, an athermal optical system was designed which works at 8-12 m, the focal length of 100 mm, F number is 2, and total length of the telephoto objective is 80 mm. The environment temperature analysis shows that the optical system has stable imaging quality, MTF is close to diffraction limit, the optical system has the character of small volume, simple structure and light. The optical power of optimized results were near the calculated results.