Measuring System of Digital-Optical Power Spectrum (MSDOPS) is a digit-optical hybrid processing system. The method of designing the system is given in this paper. It includes: Selecting the suitable detector, designing optical system and the electronic circuit. The schematic diagram of the MSDOPS is shown in Fig.l. The optical system consists of He-Ne Laser, spacial filter, collimating lens, Fourier Transform lens (FTL), and magnifying lens. Its function is to give the Fourier spectrum for the input. 64-element photo-electric detector, electric shutter, electronic circuit, and A/D converter make up the optic-electric converter. Optical signals are converted into electric signals. Digital signal processing is carried out by a microcomputer. The input image, recorded on films, can be transmitted by auto-transfering mechanism into the liquid-gate at the entrance of MSDOPS.