Based on the analysis of the features of indentation image for Brinell hardness test,the measurement of indentation diameter for Brinell hardness based on the digital image processing is put forward.Using the industrial CCD camera to catch the indentation image of the Brinell hardness,the accurate and automatical measurement of the indentation diameter is realized by the image processing steps of the image segmentation,target area processing,indentation outline fitting and so on.