Because of the large number of the lenses in a small scale projected objective, it is unsuitable to use a traditional method that each compensator only compensates the corresponding misalignment. A sensitivity matrix is utilized to solve this problem. The sensitivity matrix is decomposed using singularly valuable decomposition method. The values and signs of displaced parameters vector are analyzed, and the correlations among each displaced parameter are obtained. A method of selecting a set of optimum combination of system compensators which only need to analyze a few displaced parameters vectors is proposed. The selected compensators are proved as correct by massive simulation calculations with the aiding of macro commands modes. After the original assembling, a pre-aligning procedure of optical system is carried out to ensure the feasibility of the aligning scheme. Test results show that the wave front errors root mean square (RMS) reduced to 29.6 nm from 70 nm after compensating, which is better than the requirements of the qualifications. The results prove the methods of selecting compensators are right and effective.