In this paper,a method based on machine vision has been presented,which is used to detect the impurities and defects existing in the intake pipe of automobile engine. By establishing the module of Vision and Motion in LabVIEW and Vision Assistant,the method conducts a series of image processing,such as image preprocessing,image morphology processing,image segmentation,senior morphology processing,and develops the detection system for the intake pipe of automobile engine. Practice shows that this detection method is reasonable and the operation is convenient and practical. The visual effect is good. The detection method meets the testing requirements.