Based on the wavefront aberration

a technique expressed by Zernike’s circle polynomials was developed to test and separate the unsymmetrical error of null lens. By turning the null lens or the tested surface in different angles along their optic axis

the different testing results were obtained. According to these results

the wavefront aberration’s unsymmetrical coefficients of Zernike’s circle polynomials caused by the error of null lens were obtained

then a corrective file to correct the last testing result can be given. With this technique

the demands on the material

manufacturing

and assembly of null lens is not so critical

and the test accuracy is improved observably. The experimental results show

before and after the correction technique is used

the test result is 0.105λ and 0.026λ

respectively

and the difference among four testing results of the mirror in four different orientations is less than 0.001λ

so that the technique has been successfully applied to test a hyperboloid convex surface.