At present, on-machine measurement has received extensive attention due to high efficiency and automatic quality control. In this paper, two applications of on-machine vision measurement of metal parts were introduced. With regard to geometric measurement of small square part, four sides and angle were measured. The procedure of camera calibration, image processing and geometric representation was expounded. For medium square part, four overlapped images were captured by controlling the worktable movement. Size and shape measurement were achieved after image mosaicing. Two application results proved that this kind of on-machine visual measurement is efficient and practical.