For meeting the requirements of the high-precision telescopes, the design of collimator is essential. The diameter of the collimator should be larger than that of the target for the using of alignment. Special supporting structures are demanded to reduce the deformation of gravity and to control the surface deformation induced by the mounting force when inspecting large-aperture primary mirrors (M1). By using the finite element method, a ZERODUR® mirror of a diameter of 620 mm for a collimator will be analyzed to obtain the deformation induced by the supporting structures and adjustment mechanism. The Zernike polynomials will also be adopted to fit the optical surface and separate corresponding aberrations. The computed and measured wavefront aberration configurations for the collimator M1 will be complementally obtained. The wavefront aberrations will be adjusted by using the fine adjustment screws with the optical path differences 3D map of the mirror surface. Through the studies under different boundary conditions and supporting positions of the inner ring, it is concluded that the optical performance is excellent under a strong enough supporter. Besides, the best adjustment position has been attained and applied to the actual collimator M1 to prove the correctness of the simulation results.