Space and airborne remote sensing urgently require large relative aperture and wide fieldofview imaging spectrometer. Its telescope must have large relative aperture, wide field of view, telecentric image space, and high image quality. Based on the geometric imaging theory of commonaxis threemirror systems, the design problem of large relative aperture, wide fieldofview, telecentric offaxis threemirror anastigmatic (TMA) telescope are studied. The procedure for calculating initial structural parameter is programmed. By means of field of view offaxis, an telecentric offaxis threemirror telescope system is designed. The spectral range is 200～1 000 nm, the focal length is 210 mm, the relative aperture is 1∶2.5, and the field of view is 14°. The primary mirror and third mirror are sixorder aspheric surfaces, and the second mirror is a quadratic surface. RMS diameter of the spot diagram is less than 16 μm, 80% of the enclosed energy is in a pixel, the MTF is more than 0.75 at Nyquist spatial frequency 22.2 lp/mm, the distortion is less than 0.2%, and each specification satisfy the application requirement.