An athermalization design method of a visible light optical system is proposed based on the grouping by weight. For this optical system satisfying the requirements of image quality at normal temperature, the comprehensive weight of chromatic power and thermal power produced by each element is calculated. The structures are grouped by the comparison among the comprehensive weights, and the initial system is equivalent to two single lens systems for the choice of the optical materials. The athermalization design of a double Gaussian aerial camera with a focal length of 400 mm and an F number of 4 is conducted, whose modulation transfer function (MTF) is larger than 0.4 at a spatial frequency of 55 lp·mm -1 under the temperature in the range of -40-+60 ℃. The research results show that this design method can ensure the telephoto optical system possess good image quality and stable optical performance under the environment of large temperature difference.