Abstract: The present invention relates to a large numerical aperture phase-shifting dual pinhole diffraction interferometer and its test method, the diffraction interferometer comprises: reference light passage, test light passage and pinhole substrate; wherein, said pinhole substrate comprises test pinhole and reference pinhole; the diffracted wavefront emitted from the test pinhole would be reflected by the optical component to be tested near the pinhole substrate and converge near the reference pinhole, and said diffracted wavefront comprising surface shape information of optical component to be tested, would be reflected by the pinhole substrate and interference with the diffracted wavefront emitted by reference pinhole, forming interference fringes.