Abstract: In the applications of collimator with large diameter and long focal length, the position accuracy of the collimator objective and its sensitive tuning during the process of assembly and adjustment are very important. This paper introduces the primary mirror structure of the large-diameter optical collimator and its test method, presents the assembly and adjustment methods for optical systems with three different apertures, analyzes the primary mirror structure and tuning method of the 700 mm collimator, and uses 4D interferometer to detect the effects of assembling-adjusting device on surface shape. The results show that the assembling-adjusting device moves freely and the movement has no impact on the precision of surface shape, the pitch and rotation accuracies are better than 3 and have six degrees of freedom.