During the shield tunneling construction in composite strata, the spatial deflection of the shield machine often leads to the floating and bending deformation of the segments. In order to investigate the structural response and derivative mechanisms, this study established a three-dimensional numerical calculation model under multi-source load coupling. The spatial deformation distribution and evolution characteristics of segments were calculated and analyzed, and the external load distribution law of segment was explored through field tests. Finally, the deformation evolution mode of segments was revealed through three-dimensional laser radar testing. The research 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 will 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 of the shield shell. When the shield tail brush passes through the segment, the contact pressure of the segment is distributed obliquely and symmetrically, and the lower part is 12% larger than the upper part, and the axis of symmetry of the contact pressure is almost coincident with the short axis direction of the pipe segment. Three dimensional LiDAR point cloud measurement can accurately and quantitatively evaluate the segment deformation.