It is a common problem in precise submillimeter-wave telescopes that thermal deformation coupling between major subsystems results from materials with different coefficients of thermal expansion or at different temperatures. Here, the method of combining thermal homology theory with a genetic algorithm (CTHTGA) is proposed for the design and optimization of large precise submillimeter-wave antennas. The CTHTGA method has two key steps: (1) design of the structure of the antenna according to thermal homology theory; and (2) structural optimization based on the genetic algorithm. It has the ability to solve the problem of thermal deformation coupling well and to ensure sufficient rigidity. As an application, CTHTGA was used in the design and optimization of a 1.2 m submillimeter-wave telescope. The results showed that the CTHTGA method, compared to the previous design of a 1.2 m antenna, not only dramatically decreases the impact of thermal deformation coupling but gives the designed antenna sufficient stiffness and smaller gravity deformation. Moreover, other things being equal, a method of combining thermal homology theory with zero-order and a first-order compound optimization algorithm is used to quantitatively validate the CTHTGA method. As the results suggest, the overall performance of the CTHTGA is, to the best of our knowledge, better than that of the latter method.