Abstract: The shape of optical lightweight thin reflector possessing large flakiness ratio is always effected by wide-range temperature and harsh environment(especially at -40℃), seriously influencing the system image quality. Aiming at this problem, based on flexible support principle and thermodynamics theory, a new support structure was designed for small lightweight thin splitting reflector. The temperature adaptability of the support structure was analyzed by using finite element method, and the low temperature tests for assembled mirror components were conducted. The result shows that the accuracy of reflector surface figure remains 0.25λ(λ＝632.8 nm, peak-to-valley)at -40℃. These results demonstrate that the novel flexible supporting structure design satisfies the application environment requirements.