In order to measure the wavefront aberration of optical system with the high accuracy, the improved fiber phase-shifting point diffraction interferometer was introduced, its working principle was introduced, and the parameters of the key components of the interferometer including laser source and fiber were selected and analyzed. After the test, the laser power stability was about 1%(10 min), the spot size was in the allowable range of the optimum coupling efficiency, the beam position stability was about 6 μm, the coherence length was about 1 cm, the above were all in the allowable range of testing accuracy; No polarization-maintaining single-mode fiber was selected, its core diameter was 3.5 μm, the fiber endface was coated transflective metal film, the high fringe contrast and light energy utilization were realized, and the wavefront reference source was designed, it′s convenient for the polishing, coating and clamping of fiber endface. Finally, the selected components were used to build experimental device of fiber phase-shifting point diffraction interferometer, above works provide preparation for ultimately achieving high accuracy test of the wavefront aberration of optical system.