Objective To study the effects of the various thickness of periodontal ligament on stress and displacement of mandibular first molar and periodontal tissues during mesial movement of tooth in lingual orthodontics. Methods Based on the reverse engineering technology, the three-dimensional assembly models of the teeth, periodontal ligament and alveolar bone with the same height of alveolar bone were constructed, and thicknesses of the periodontal ligament was 0.15, 0.2, 0.25, 0.3 and 0.35 mm, respectively. The stress and displacement of periodontal ligament, root and surface of alveolar bone were analyzed under the condition of lingual tipping, rotation and translation movements. Results For the maximum stress of periodontal ligament, root and surface of alveolar bone due to different periodontal ligament thickness, the ratio of the maximum value to the minimum value was 1.46, 2.06 and 6.72, respectively. For the maximum displacement of root and the surface of alveolar bone, the ratio of the maximum value to the minimum value was 1.65 and 1.50, respectively. Corresponding with different thickness of periodontal ligament, the location of the maximum stress of root and periodontal tissues would change at root, periodontal furcation and tooth neck. Conclusions In clinical practice, changes of tooth neck, periodontal furcation and root should be observed carefully, and the translation movement is more conducive to the health of teeth and periodontal tissues for patients with thin thickness of periodontic ligament.