As the most critical step in the construction process, the rotating precision of large-tonnage bridge requires high accuracy and advanced technology. As a basic parameter, the reliability of its precision is significant to the calculation of the unbalance moment of the rotating bridge. In order to obtain the key parameters of the rotating bridge accurately, a new method based on 3D laser scanning and BIM reverse modeling technology is proposed to obtain the self weight and unbalanced moment of the rotating bridge. Based on the project of Kunming Chuxiong expressway, Dade bridge in the transition section is taken as the research object for experimental demonstration. The results show that the point cloud and the reverse BIM model obtained by this method can avoid the inconsistency between the surface deformation and the theoretical design caused by the environmental factors of the rotating bridge. It improves the efficiency and reliability of obtaining the parameters of self weight and unbalanced moment, and further guarantees the balance and safety of large tonnage bridge in the process of turning.