Large aperture transport mirror is a typical unit in the high power solid- state laser system. Firstly, the principles of large aperture transport mirror′ s wavefront errors are discussed in detail, according to an analysis on its structure and assembly characters. Then, the fundamental mechanics model to evaluate the surface deformation of mounted mirror is given. And furthermore, a technical framework combined with the methods of field optical measurements and 3D numerical modeling is proposed to predicate the surface profile of spatial installed mirror. The proposed method is verified with a case study. And some assembly problems in SG-III′s transport mirror are also discussed.