An all-reflective system with compact structure and wide field-of-view is designed on the basis of the three-mirror aberration theory.Coaxial design is adopted whereas its off-axis rays is used,so that the length of its lens barrel can be of f′/7～f′/9,field-of-view more than 3°,the obstruction ratio less than 6%,and the image of quality reaches to the limit of diffraction.The optical system suits the needs of long focus remote sensing CCD camera.