A new method for workpiece surface roughness measuring system based on machine vision technology was designed. A Charge-coupled Device （CCD） camera was used to take workpiece surface image. Then median filtering, image enhancement and image binarization techniques were used for image preprocessing. And then useful information was extracted from image characteristic parameters. The surface roughness of cutting workpiece was calculated out. Researching emphasis was focused on the hardware design and software programming of the main two parts, image acquisition module and image processing module. This measuring system was used to measure cutting workpiece surface roughness, and perform very well.