In order to evaluate surface of large aperture reflecting mirror, the Randon transformation is used to represent the area structural function collapse. The evaluation ways of algorithm for collapse are studied, and the specific step is expressed. Then this method is applied to the Zernike polynomial which can simulate the wave front perfectly. The algorithm is applied to the meter rank reflecting mirror and tertiary mirror of 30 m telescope (TMT) simulating data, the correctness and feasibility of the algorithm are certified. This research will supply good instructions at the design, measurement and manufacture of large mirrors, and will do good to the complement of tertiary mirror of 30 m telescope.