Images processing technologies were used of digital image segmentation and subpixel edge detection. The boundaries of tool wear were measured automatically, and the amount of wear and blunt standard was compared to judge the wear condition of tool, achieving tool wear for intermittent automatic measurement online. Aimed at edge features of the tools, the digital images processing technologies were used like median filter, contrast stretching, iterative adaptive binarization, based watershed segmentation, Roberts edge operator, image matching, zernike orthogonal moments and curve fitting, and etc. The detection of tool wear condition is completed with micron level high precision.