In this paper, straight edge cutter is introduced to machine circular arc tooth belt pulley. General method of fitting circular arc with straight line was set up, and function expression of the fitting straight line was solved. By fitting theoretical contour shape of cutter for processing circular arc tooth belt pulley and contour shape of straight edge cutter, profile error formula of straight edge cutter was obtained. And fitting calculation was carried out with the maximum profile error (i.e. fitting the maximum error) on axial profile of cutter as a fitting condition. Finally it was verified with processing examples.