The sptitching measuring method applied in large-aperture aspheric surface optical elements can expand the range of precision measuring instrument. And the key point is developing the technique for high precision measuring data processing. To deal with the problem of cumulative errors which existed in the process of multi-section stitching, datum-transformation method was proposed, according to the characteristic of stitching measurement. The stitching measuring experiments were carried out based on Talysurf PGI 1240 profilometer of Taylor Hobson Company to verify the purpose for eliminating cumulative errors. The results show that datum-transformation method is feasible with the characteristic such as fast speed, high precision, and good operability.