Temperature filed distributing of a high resolution space telescope is analyzed by thermaloptical method based on optical frontwaveerror theory, and thermal contral target is ascertained. The thermal tests in the vacuum are carried out to validate the analysis. Tests results indicate that the ideal focal plane position vs temperature level are linearity, and changes scope approximately 0.08～0.1 mm·℃－1. As the macrocosmic temperature changing within (20±1)℃, system MTF change about 0.02. When the temperature grads are more than 2 ℃ in axis direction and diameter direction, the ideal focal plane position departure happenes and the MTF decline obviously if unfocus.