In NC milling process, tool wear has great influence on the machining quality of product. In this paper, a mapping measurement method is used to obtain tool wear and a data processing method is proposed to deal with the data getting from the measurement. First, tool wear along radius of tool’s cross-section, which is called radial wear, can be obtained by mapping measurement method. Then tool flank wear can be easily calculated based on the established relationship between radial wear and flank wear. In order to get radial wear, we process those measured data that are obtained from mapping measurement. In this process, least square method is adopted to fit these data to get the radius of section circle at a certain position. So the radial wear can be obtained by comparing the radius of the fitting circle and the original radius of tool at a certain section. Finally, the data processing software is realized by using Visual C++ development tool according to the designed data processing method of tool wear.