During the shield tunnel construction in composite strata, there are complex interactions between the shield machine and segment due to spatial posture deflection. Causing multidimensional deformation response in various parts of the segment, resulting in extreme floating displacement and segment dislocation. In order to investigate the structural response and derivative mechanisms, this study established a three-dimensional numerical calculation model under multi-source load coupling. Finally, the spatial deformation distribution and evolution characteristics of segments were calculated and analyzed by field 3D LiDAR testing. The results indicate that under the spatial deflection, 64% of the long-axis deformation of the segment occurs before detaching from the shield tail completely, and the long axis deflection is opposite to the circumferential rotation of the shield shell. In addition, 50% of the average increase in longitudinal rotation angle of the segment occurs after the segment detaching from the shield tail completely, while 44% of the increase in circumferential rotation angle occurs during the gradual detachment from the shield tail. During the entire process, the continuous development of circumferential displacement of the segments is mainly caused by the circumferential rotation of the shield shell, and after the segments completely detaching from the shield tail, their radial displacement development and shape changes are mainly affected by their own circumferential displacement changes. The lateral rotation of the shield shell would promote the longitudinal displacement of the segment in the same direction. After detaching from the shield tail, the further development of its longitudinal displacement is mainly affected by the longitudinal deflection. 3D LiDAR point cloud measurement could accurately and quantitatively evaluate the segment deformation.