Because of the coupling that exists in obscuration interferogram fitted with Zernike circle polynomials,the Seidel aberrations computed with Zernike coefficients will be inaccurate.Based on the "Mask" function provided by interferometric reduction software,a series of obscuration interferograms with different obscuration ratio are constructed,and the corresponding coefficients fitted with Zernike circle polynomials are calculated.Combining with own software,whether the obscuration ratio of the tested aspherical mirror is beyond the threshold for every Seidel term is estimated,and the operating flow is provided in detail.We tested and analyzed a 700 mm paraboloid primary mirror with 0.23 obscuration.The experimental results show the optimum method is simply feasible,and the estimated values of Seidel aberrations are more accurate.There needn't the complicated data conversion and polynomials fitting in own software,based on the standard interferometric reduction software.