Using a computer-generated hologram as a compensator to fabricate concave holographic gratings is more flexible in both aberration correction and wavelength selection in comparison with traditional method. In this paper a method of defocusing filtering with a cylindrical wave front used as a reference beam is discussed. With this method, the space-bandwidth product of GGH is obviously increased, thus greatly increasing the range of usage. Using such CGH compensators, 12001/mm concave holographic gratings, both type III and IV，have been, fabricated. Experiment results are preranfced.