The optical simulation analysis and computer-aided alignment are carried out to solve the problems of multidegree of freedom, multichannel and complex alignment of optical components for off-axis three-mirror multispectral space camera. According to the results of the optical design, a field aperture based on ray tracing is designed, the wavefront aberrations of the infrared channel and the visible channel are given, and the sensitivity matrix of the secondary mirror and the third mirror is simulated and analyzed. The total reflection infrared channel is aligned with a visible-light interferometer. According to the Zernike aberration coefficient obtained by the interferometer, combined with the computer-aided alignment simulation results, the spatial position relationship between the secondary mirror and the third mirror is adjusted based on the primary mirror until the wavefront of the system meets the design requirements. The Root Mean Square (RMS) alignment results of the center field-of-view and the edge field-of-view of the infrared channel are 0.15λ (λ=632.8 nm) and 0.33λ respectively; the RMS values of the center field-of-view and the edge field-of-view of the visible channel are 0.06λ and 0.07λ respectively. Considering the processing and assembly errors, the alignment results are basically consistent with the design results. The on-orbit image of the camera is clear and the image quality is high.