A 635 nm and 10.5 μm dual-band coherent optical infrared transmission interferometer was designed. This integrated system employs a visible semiconductor laser at 635 nm and an infrared semiconductor laser at 10.5 μm as the interference light source. Through tests with this integrated system, a common optical path between the interference of the visible light band and the infrared light band could be determined. The common mode of the mechanical phase shift system and the visible light co-alignment were used in the dual-band optical path, and the phase shifter long-stroke error was calibrated at 10.5 μm based on the segment stagnation point of the 635 nm testing light. The accuracy of the developed dual-wavelength infrared interferometer system was measured, where the values of PV, RMS, and RMS repeatability were better than 0.05λ, 0.01λ, and 0.001λ, respectively. The interferometer was used to test an aspherical mirror with off-axis amount of 800 nm and dimensions of 400 mm×400 mm, where the maximum deviation of the measured edge value is 21.9 μm. Furthermore, the interferometer enables high-accurate surface measurements during the entire grinding process of large-aperture off-axis aspheric components.