OBJECTIVE To investigate the biomechanical changes of internal midface distraction after different types of maxillary osteotomy in patients with cleft lip and palate (CLP). METHODS 3-D finite element (FEM) analysis was used. 3-D models of Le Fort I, II, III osteotomy and soft tissue were established. Based on the new pattern of internal midface distractor, the distraction of maxillary complex was simulated to advance 10 mm anteriorly. The mechanical change was studied. RESULTS The maxillary complex in CLP were advanced after distraction. Constriction of alveolar crest and palate occurred in Le Fort I osteotomy, but not in Le Fort II and III osteotomy. The maxillary complex was moved anteriorly en bloc after Le Fort III osteotomy, but some degree of rotation of maxillary complex was observed during the distraction after Le Fort I and II osteotomy. In vertical direction, the maxillary complex had more counterclockwise rotation after Le Fort II osteotomy. CONCLUSIONS 3-D FEM analysis can be used for the study of internal distraction. It can reflect the maxillary movement and provide the theory basis for preoperative design.