Abstract: In order to solve the problem evaluating the stitching accuracy of large-diameter reflecting mirror, a kind of stitching accuracy evaluating method called self-test was proposed in the article, realizing the analysis and evaluation to the stitching accuracy of large-diameter reflector mirror, while providing a method measuring the stitching precision. Self-test was a kind of method testing the accuracy of stitching result with sub-aperture measuring result. In the article, relative accuracy evaluation indexes and their calculation methods were discussed. As a project example, 800 mm plane mirror was splicing measured with a 600 mm interferometer and stitching accuracy was evaluated with the self-test method. It shows that the stitching is accurate and it's reliable and precise to assess stitching accuracy by the way of self-test at the same time.