The invention provides a device for aligning, assembling and adjusting optical systems and a method thereof. The device comprises an auto-collimate microscope and a turntable with an air bearing, wherein the optical axis of the auto-collimate microscope is accurately aligned with a rotation shaft of the air bearing, the auto-collimate microscope comprises a lighting module, a mask board with carved lines, a beam splitter prism, a focusing objective lens group, a microscope objective lens group, a spectroscope, a measurement reticule, a CCD and a microscope eyeglass group, to confirm the eccentricity measurement accuracy and lens assembly and adjustment accuracy of the device. The device can be applied in high accuracy centering machines to fit the high accuracy air bearings, thereby effectively improving the centering accuracy of the centering machines and satisfying the lens assembly and adjustment demands of high accuracy optical systems.