A MATLAB based software package called QUANSMIC(quantitative analysis system of microcracks in concrete) including image binarizing module, shape analyzing module, crack skeletonizing module and automatic measuring module was developed to automatically extract and quantitatively analyze the microcrack characteristics(such as area, length, width, etc) in the microscopic images of concrete slices, in which the microcracks were highlighted with vacuum fluorescent epoxy impregnation technique. The Intermodes method was employed to determine the grayscale threshold in the binarizing module. The noises were removed by opening operation and the aspect ratio(ratio of length to width) was set at 20 to distinguish voids from cracks in the shape analyzing module. The macro orientation of the skeletonized microcracks was considered in length measurement in the automatic measuring module to reduce relative errors. QUANSMIC could provide a powerful tool of quantitatively damage evaluation and health diagnosis of concrete based on digital image processing techniques.