Abstract: A digital image processing technique based on measuring method of foamed dreg edge was described. The video signals of foamed dreg obtained by CCD camera were converted into digital image signal by an image acquisition card. The contour line of foamed dreg was obtained by image processing of computer, the actual height of foamed dreg was observed by the graduation line of contour line background. The experiment evinced that the method was feasible on principle and have directive meaning for realization of on-line measurement of foam height on site.