Large aperture optical element clamping generally use the traditional organic stress- free clamping. In vacuum environment, the clamping will bring about various problems such as the organic pollution. A fixture scheme and the corresponding fixture have been designed for large plane optical element. The scheme uses the metal structure for clamping optical element directly, reduces surface machining accuracy of metal frame, achieves stress- free clamping and avoids organic pollution caused by traditional way with the optical element working at any angles. This scheme can be widely used in the large aperture optical elements clamping in optical engineering and optical experimental device.