Holographic spatial reconstruction technique is an important approach to display three-dimensional(3D) images because the amplitude and the phase of object wave can be recorded in a single hologram

and then 3D image can be reconstructed in free space. Hologram calculation of three-dimensional objects is a key part of holographic spatial reconstruction technique. The basic theories for computer-generated hologram(CGH) calculation of 3D objects were described firstly. Then the principles and key techniques of several typical approaches for CGH calculation of 3D objects were analyzed. Three types of CGHs were calculated for 3D objects by use of tomography approach

Fresnel zone approach and multi-view image synthesizing approach. Subsequently

electro-holographic display experiment was performed by inputting CGH of 3D object calculated by tomography approach into LCR-2500 spatial light modulator and using diode laser with wavelength 650 nm and power 150 mW. Numerical reconstruction results were also obtained from the CGHs calculated by other two approaches. Then the characteristics and limitations were analyzed for the existing methods of three-dimensional CGH calculation. Some key problems associated with hardware and algorithms were also analyzed

and the approaches were discussed for improving the calculation efficiency and the quality of CGH.