As an ideal 3D display way， holographic 3D display can present the same information of depth and parallax as real objects. However, the computer-generated hologram for a 3D object has to do complex and massive computations, how to create a computer-generated hologram quickly for the 3D object has become a key problem in the digital holographic 3D display technique. In this paper, the key techniques of digital holographic 3D display are discussed firstly, including three kinds of methods for creating computer-generated holograms like object point scattering, holographic stereograms and holographic tomography, a RGB separating method for colorful holographic 3D display, and several kinds of improving quality methods for reconstructed images. Then, few latest holographic 3D display systems and key devices are analyzed technically. Finally, it summarizes the present state of the digital holographic 3D display technique and points out that the technology will develop to real-time, dynamics, larger sizes and higher resolution.