Abstract: To meet the high precision requirement of complex space optical systems, and to overcome the limitations of traditional benchmark pass method and computer-aided adjustment technique individually for the complex reflection optical systems with three or more mirrors, a new alignment technique by combining above two methods is proposed. An alignment experiment is performed on the optical system with multiple mirrors by the proposed method. The results show that the alignment technique of combined two methods is effective and reasonable. The misalignments of the mirror in the Y and Z directions have been decreased from 18.651 mm and 9.879 mm to 1.036 mm and 0.102 mm, respectively, and the system wavefront aberration has reached the average value of 1/14(RMS) in a full field. The method is proved to be guidance capability and practical reference for complicated optical systems with multimirrors, which can effectively reduce the alignment time and achieve higher system accuracy.