The ossification's degrees of the midpalatal suture were in stage A, B or C The width of the upper dental arch was narrower than lower dental arch - 3.51 mm (intermolar) and - 2.21 mm (interpremolar); the maxillary width at the first molar was smaller the mandibular width 2, 68 ± 1, 81 mm according to the Yonsei index Conclusion: the age of maxillary contriction patients treating with rapid maxillary expansion are in growing stages, the ossification's degrees of the midpalatal suture are incomplete closed stage, the maxillary is narrower than mandible when measure on plaster model and CBCT film.