with the development of space and aviation industry, the optical systems with high resolution and better imaging quality are required. according to the alignment technical process, the factors of every step which have big influence to the imaging quality are analyzed. it is detected that the micro-stress assembly of the optical unit and the high co-axial precision of the entire optical system are the two important factors which are supposed to determine how well the imaging quality of the optical system is; also the technical methods are discussed to ensure these two factors from the engineering view. the reflective interference testing method to measure the surface figure and the transitive interference testing method to measure the wave aberration of the optical unit are combined to ensure the micro-stress assembly of the optical unit, so it will not bring astigmatism to the whole system imaging quality. optical alignment machining and precision alignment are combined to ensure the high co-axial precision of the optical system. an optical lens of high accuracy is assembled by using these methods; the final wave aberration of optical lens is 0.022 lambda.