In the printing industry, printing dot parameters are measured by means of obtaining the values of area, distance,angle of printing dots to control printing quality. Because the traditional measuring instrument in the measuring network area is based on optical measurement and indirect conversion of light into density value, there is measurement error and calculation error which affect the printing quality. In this paper, a printing measuring instrument is designed on the basis of digital image processing whose measuring is direct. Its measuring accuracy is higher and it is more helpful for controlling printing quality.