The interferometer is an indispensable instrument in the modern optic manufacture and testing, whose testing accuracy limits the manufacture accuracy of the optic. In theory, the point diffraction interferometer, which use the wave-front diffracted by a pinhole as reference wave, can be applied in the sub-nanometer optical testing. The deviationbetween the wave-front, which is diffracted by the pinhole with shape errors, and the ideal spherical wave-front is calculated based on finite element method. The main aberrations of the diffracted wave, induced by the shape errors, are also analyzed. When the axes of the pinhole are 380 nm and 320 nm, the deviation is 0.9e-3 λ.