In order to extend the depth of focus of optical systems, an optical-digital system using wave-front coding technology was established.By adding a phase mask at the aperture stop of a general optical system combined with post-digital processing, this system extended its depth of focus greatly.Firstly, the proposal, development and theoretical basis of wave-front coding were briefly introduced; then, a triplet system with a cubic-phase-plate was designed, and the imaging characteristics of the traditional system and wave-front coding system were analyzed using CODEV.Furthermore, the three-dimensional contour maps of Point Spread Function (PSF) and the Modulation Transfer Function(MTF) curves within defocus of ±40 times were obtained.Finally, the imaging experiment of manufactured system was carried out, and the images of a traditional system and a wave-front coding system before and after decoding were compared.The results show that the wave-front coding system can extend the depth of focus by 40 times compared with the traditional system while maintaining the light flux and image plane resolution.