In order to realize the high accuracy alignment of co-axial eccentric-pupil three-mirror system, and to improve the image quality, the micro-stress installation of large-aperture aspheric mirror and system benchmarking adjusting techniques are investigated. The optical calibration and mechanical calibration of primary mirror, secondary mirror and third mirror are unified by using optical alignment machining. The assembly of three mirrors, also the aberration adjustment of two-mirror system and three-mirror system are realized by the instruct of wavefront aberration distribution which is gained from Zygo interferometer. The pupil of coaxial three-mirror system is eccentric, and the sweeping direction is vertical with the linear charge coupled device (CCD) direction, the system astigmatism brought by the tilting of folded-axis mirror is removed by rotating the folded-axis mirror and trimming the neighboring circle. Alignment results indicate that the image quality targets of optical system′s each field-view are achieved, the root mean square (RMS) of optical system is less than 0.07λ, and the modulation transfer function (MTF) is larger than 0.57.