Objective To study the mechanisms of vertebrae semi-dislocation of Tuina manipulation for treating patients with lumbar intervertebral disc protrusion (LIDP) by observing the three-dimensional (3D) displacement of lumbar before and after Tuina manipulation. Methods Ten LIDP patients were selected and evenly divided into two groups: Group 1 as tendon-smoothing manipulation group (relaxing group), Group 2 as tendon-smoothing plus adjusting manipulation group (adjusting group). Besides, Group 3 as control group was established by 5 healthy volunteers treated with tendon-smoothing manipulation. Before and after manipulation intervention, all subjects were scanned from L1 to L5 segment by using Philips 64 spiral CT under equal conditions for accessing the volume data. ITK reconstruction software was used to reconstruct each lumbar skeleton for finite element analysis. The 3D displacements and angular displacements among three groups were compared. Results 3D displacement from L1 to L5 segment all changed in three groups. For adjusting group, the angular displacements at X-axis in L3 segment was (1.77±0.46)°, and that in L4 segment at X-axis and Y-axis was (1.78±0.53)° and (1.89±0.75)°, respectively, which was significantly larger than relaxing group and control group (P<0.05); the angular displacements at X-axis from L1 to L5 segment were (1.50±0.47)°, (1.55±0.57)°, (1.77±0.46)°, (1.78±0.53)°, (1.61±0.39)°, respectively, which were significantly larger than control group (P<0.05); displacement at Y-axis in L3 segment was (2.87±0.74) mm, and that at X-axis in L4 segment was (1.68±0.64) mm, which were significantly larger than relaxing group and control group (P<0.05); displacement at X-axis in L1, L4 and L5 segment was (1.28±0.21),（1.68±0.64）, (1.30±0.51） mm, and that at Y-axis in L1 to L3 segment was (1.92±0.42), (2.25±0.61), (2.87±0.74) mm, which was significantly larger than control group (P<0.05). The angular displacements and displacements of L1 to L5 segment in relaxing group were larger than those in control group, but without any significant differences. Conclusions Compared with relaxing manipulation, adjusting manipulation played a more obvious adjusting role in instability and degenerative lumbar vertebra, especially for angular displacements in X-axis, and displacements in X-axis and Y-axis. Namely, the mechanisms of vertebrae semi-dislocation of adjusting manipulation were to make horizontal and rotational displacements at lumbar vertebra other than upper and lower displacement. The effect of relaxing manipulation was not so obvious on lumbar structure of LIDP patients.