Abstract: By calculating the nonuniformity in overlapping area between sub-apertures, errors such as positioning error, system error and stitching model pattern that affect the stitching testing prelision of large aperture continuous phase plate(CPP) are summarized and analyzed. Some results indicate that positioning errors are the major reason affecting the stitching precision and the nonuniformity in overlapping area could be decreased as the system errors are handled effectively. Furthermore, there is no more obvious difference in the choice of stitching pattern concerning the stitching result. The statistical result shows that the root-mean-square of the residual error(ERMS) raises in the overlapping area as the increment of depth as CPP's wavefront at the testing level of pixel, which means that the stitching testing precision declines simultaneously.