A computer generated holography (CGH) wavefront transforming element is designed and fabricated based on computer generated hologram and binary optical technique,and is applied in head up display. Its diffraction efficiency is very high. The diffraction efficiency of a two phase CGH is four times higher than that of a general CGH. It can generate special optical wavefront, such as aspheric surface, ring shaped surface, cone shaped surface and so on,which the traditional optical elements can not generate. Moreover, the fabrication and duplication techniques of CGH are simple and convenient.