In order to achieve fast error alignment in concentrator mirror unit installation, a mirror unit supporting-adjusting structure consists of threaded vice and ball joint is designed to precisely control the adjusting amount. A fast measurement method of mirror unit posture (axis vector and vertex position) and a quantitative alignment method of axis vector posture error are proposed. Firstly, the photogrammetry method is applied to determine the three feature points (construct a triangle) coordinates in the mirror unit surface. Then, an association mathematical model of the ball joint center coordinates, the mirror unit posture, and the feature points coordinates is established to achieve fast measurement of the mirror unit posture. After that, combined with the mirror unit alignment process, we propose the “three rotational-one moving” rigid body motion (three rotate around axis and one moving) to equate the mirror posture error. The mirror unit posture associated with the bolt adjusting quantity model is established to achieve the quantitative alignment of mirror unit axis vector error. Finally, the convenience of the mirror unit supporting-adjusting structure and the effectiveness of the axis vector quantity alignment method are verified by the virtual alignment experiment established by SolidWorks software and metal flat surface posture alignment experiment in door. The proposed mirror unit alignment method is not restricted by the reflector geometry and it has extensive applicability.