To solve the core problem of how to search and converge to the feature points faced by the automatic knife-edge instrument, this paper proposes an aspheric surface testing technology based on the axial movement of the knife-edge instrument to realize the extraction of ring-belt errors during the search process. By this technology, the wavefront characteristics are dynamically obtained during the search process, and the convergence can be accelerated to find the feature points. The mirror ring-belt errors of different parameters are tested, and the relative error between the tested ring-belt error position and the test result of the interferometer is less than 3.3%, which verifies the effectiveness of the method. The proposed method provides a convenient solution for the automatic measurement of the knife-edge instrument and provides technical support for further improving the efficiency of aspheric surface processing.