To solve the problem of simultaneous detection of pit defect and other planar defects, a pit defect detection method based on single linear CCD system is developed. On the basis of light radiation, light illumination and camera imaging model, the mathematic model for pit detection based on single linear CCD system is deduced. The mathematic model indicates the relationship of image pixel gray level and pit depth. By making use of the structure of special light source and illumination angle, the surface pit defect can be detected. The experimental results show that the gradual change of pit edge depth causes the gradual change of CCD output voltage signal, and then causes the gradual change of pit image edge gray level. The lower the illumination angle, the more obvious the image feature. The image feature of edge pixel gray level gradual change becomes the most important feature for the distinction of pit defect and other planar defects, which contributes to the pit defect detection and recognition.