To solve the problem of the high cost of infrared detection devices in wave aberration detection, a single-detector infrared Fizeau interferometer optical path design method is proposed, which realizes that the interferometric imaging optical path and alignment imaging optical path share the same near-infrared detector and all components of the system are of existing. Based on the principle of Fizeau interference, the near-infrared fiber laser with a working wavelength of 1310 nm and the selection of a near-infrared detector with a 12.8 mm×10.24 mm target surface, combined with the measurement aperture requirement of 20 mm, the vertical of the interferometric imaging optical path is established. The axis magnification is 1/2, and the field angle of the alignment imaging optical path is ±1.2°. Combined with the laser numerical aperture of 0.14, the F number of the collimated optical path must be greater than 3.54. In this paper, the basic parameters of the imaging element are determined by calculating the conjugate relationship of the collimated optical path, the interferometric imaging optical path, and the alignment imaging optical path.First, the conjugate relationship between the collimated optical path, the interferometric imaging optical path, and the alignment imaging optical path is calculated to determine the basic parameters of the imaging element. Thorlab's cemented lens in the near-infrared band is selected as the optical element. Considering the ability of a single lens group to correct aberrations in the worst case, the collimating mirror and the imaging mirror are constructed using a double lens group.The interferometric imaging optical path is mainly composed of a light source, a collimating lens, a pinhole, an imaging lens, and a detector. To eliminate the influence of parallax and ensure that the imaging optical path has a constant magnification, the interferometric imaging optical path adopts a double telecentric design. Among them, the imaging lens consists of a single lens group and a double lens group. Compared with the single lens group, the image quality of the double lens group is significantly improved. The scheme of the double lens group can control the RMS of the full field of view within the diffraction limit. The RMS value of the wave aberration in the full field of view of the two-group scheme was less than 0.03λ; the maximum astigmatism of the system was reduced from 4 mm to 0.17 mm; the maximum field curvature was reduced from 2 mm to 0.08 mm; maximum distortion was reduced from 1.6% to 0.7%. For the field curvature distortion of the two-group scheme, with the spatial frequency of 25 mm/lp as the comparison index, the MTF values of the full-space sagittal and meridional directions are both less than 0.3; the MTF value of the two-group scheme is about 0.5 when the almost identical to the meridian MTF value. The system finally uses a double lens group composed of double 200 mm achromatic cemented lenses as the collimating lens for the collimating optical path. The light sources are located at the focal plane of the collimator lens, 94.5 mm apart, the aperture diaphragm is 40.2 mm from the imaging mirror, and the imaging mirror is 55.6 mm from the detector.The alignment imaging optical path is composed of the diffuser, the relay lens, the imaging lens, and the detector. After the design of the interferometric imaging optical path is completed, the distance from the image plane in the alignment imaging optical to the rear surface of the imaging lens group is a fixed value. To clearly distinguish the interferometric pattern from the spot, this paper introduces a relay lens into the alignment imaging optical path, cooperating with the imaging lens to make the optical path meet a certain lateral magnification and control the size of the spot, and finally realizes the distinction between the two. Then insert beam splitters and reflectors at the corresponding position to realize beam splitting and beam combination of the optical path.The final design of the interferometer has an effective aperture of 20 mm and a measurement error of fewer than 1/20λ, which ensures the accuracy of wave aberration detection and the requirements of aperture, while effectively controlling the cost of development.