Abstract: Objective To study the changes of the dental occlusion and the maxillofacial region after treatment with FR-Ⅲfor crossbite in children in deciduous and mixed dentition phases. Methods Sixty-four children with crossbite in deciduous and mixed dentition phases were included in this study. Tooth models and Schuller’s position and lateral head X-rays were measured before and after treatment with FR-Ⅲto study the changes in the three-dimensional structures of the dental occlusion and maxillofacial region. Result The width of dental arch exhibited little changes after the treatment whereas the length of the maxillary dental arch was increased. The upper incisors grew in labial inclination and the condyle withdrew to its natural position. The relationship of maxillary and mandibular base bone was obviously improved after the treatment, which also promoted the lingual inclination of the lower incisiors and the decrease of the genial angle. The lower and posterior facial height was increased. Conclusion FR-Ⅲ readjusts the muscle function of oral and maxillofacial system and promotes normal development of the dental arch and jaw.