The design of a diffractive reflective hybrid singlet is presented to replace a conventional doublet telescope objective. As the telescope objective has a large relative aperture (1/2.5) and a small filed of view, its spherical and lateral chromatic aberrations are high and should be corrected, while its aberrations relative to the field of view, such as astigmatism and distortion, are natually small. According to the analyzation of the primary aberrations of a hybrid singlet with a plano convex substrate, the design method of the original configration is studied. A hybrid singlet in visible band (λ from 656.3 nm to 486.1 nm) is successfully designed. In comparison with the traditional construction, this hybrid singlet, with much smaller monochromatic aberrations and nearly equal chromatic aberrations, has lower weight, greatly simplified configuration and only one material K9 used. It shows that the application of hybrid singlets in visible band is promising.