A testing method was proposed for the diffraction wavefront produced by a pinhole mounted in a point-diffraction interferometer. The producing principle of the point diffraction wavefront was presented, and the relation among the pinhole states, illumination adjustment and the wavefront aberration was analyzed. On the basis of the fundamental theory of information optics, the Fourier transform and an iterative algorithm were used to calculate and analyze the pinhole diffuse image, retrieve the phase of diffraction wavefront and then to obtain the wavefront information. The related theory was discussed and the measured point diffraction image was analyzed through a computing software of phase retrieval. Results indicate that the output phase tends to a convergence after about 15 iterations, and the image error factor has dropped to 0.12. The testing method has been applied to the selection of pinholes and the assembly of pinhole illumination systems, and experimental results prove that the testing method is valid.