Interference microscope objective is a key component of interferometric microscopy, which is widely used in the measurement of three-dimensional topography of micro-nano-surface. In this paper, an infinite conjugate large magnification Mirau interference microscope objective is designed, with the magnification ratio of up to 50× and the numerical aperture of 0.5. Based on the characteristics of the long working distance of the system, the interference objective lens adopts the retrofocus objective structure. According to the second-order spectral theory, the secondary spectral aberration correction of the interference objective is analyzed, and the glass materials and lens initial structure are selected rationally. The optical system is optimized by utilizing the optical design software Code-V. The design results show that the modulation transfer function at 800 lp/mm is more than 0.3 in the whole field of view of the optical system, and other indexes all meet the design requirements. By non-sequential modeling, optical tracing of the designed interference objective is carried out, the clear Newton ring interferogram is obtained by simulation and analysis. Which proves the rationality of the design.