Abstract: Aiming at the problem of automatic measurement of piston oil chamber，this paper studies an piston oil chamber image measuring method based on CT image．In order to evaluate the quality of each piston oil chamber，an industrial CT is used to obtain the piston oil chamber information and extract the distortion and position of oil reservoir through image processing． Considering the problem that the oil chamber affects the image edge detection precision， maximum variance separate method and median filtering method are adopted to preprocess the image．The software LabVIEW was used to authors measuring softwere, and the piston was dissected to measure oil chamber as comparative experiment. Experiment results show that the proposed method based on CT image is stable and reliable，high precision measuring of piston oil chamber is achieved，which makes a quality evaluation for piston oil chamber automatic measurement．