A new technique of digital holography is proposed, which can make the holograms with large viewing angle. According to the theory of two-step rainbow holography, rainbow holograms H1 are generated by computer and the new algorithm of mirror image is proposed which can fold the holograms with large dimension into little ones. After the downsizing by taking pictures, a hologram with high density is made. When H2 is made on optical setup, two right mirrors must be matched in order to returning the reconstructed wave to the original condition. The advantages of both computer generated holograms and optical holograms are adopted in this technique. The technique of mirror image can successfully make the holograms with large viewing angle. The principle of the proposed method and the experimental result prove that the technique not only resolves the problem on the output of holograms with large dimension and reduces the data volume greatly, but also breaks a new path for hologram three-dimensional display.