In recent years, it has been proposed that the multi-sale analyses are applied to structural design in order to reduce the development period. Though the various multi-scale analyses have been mainly applied to dynamics, they do not approach the subject in a thermal problem, which is the important analysis of structural design. Then, we have dealt with the formulation and the programming for the unsteady heat transfer problem by using mesh superposition method spotlighted in the stress analysis field. By comparison our proposed method with the traditional FEM, it has been verified that the developed program has good accuracy and the proposed method is usefulness to the structural design.