The working principle of universal tool microscope is discussed in this paper. A technique of division of scale pulse for optical prating transducer measuring system and a method of division of scale pulse between grating space by A/D are put forward. The calculating expressions of the scale pulse equivalent and the error analysis are given by mean of 8 bits A/D converter and 8 intervals in grating space.The experiments indicate that this method of division of scale pulse is valuable to practical use.