An electroholographic display is a three-dimensional (3D) display, using electroholography, for recording and reconstructing a 3D object. An electroholographic display has advantages as compared with other 3D displays; for example it can reconstruct 3D images with full parallax. However, an electroholographic display requires complex design and development of the optical system. In this paper, we report our computer aided design (CAD) tool for developing an electroholographic display. By calculating the diffraction of light, the CAD tool can rapidly evaluate a 3D reconstructed image from an electroholographic display system without developing the actual system.