In this paper a new method to fabricate concave holographic gratings is presented in which a computer-generated hologram (GGH) is used as a compensator to modulate one of the collimated beams in the optical system. The priority of this method compared with the traditional one is discussed. The arithmetic expressions for designing such a CGH compensator have been derived. Using this compensator, a 600 l/mm concave holographic grating has been fabricated. The optical system and experimental results are also presented.