Abstract： Objective To analyze the biologic principle of orthodontic treatment in patients with skeletal Class Ⅲ malocclusion and open bite.Methods Eleven pre-adolescent patients with severe skeletal Class Ⅲ malocclusion and open bite(age range 7-9 years old,mean age 8.3±0.8)were included.All patients were surgical cases but the patients rejected surgery.The theatment methods used were face mask,rapid maxillary expansion occlusal splint and fixed appliance.Lateral cephalometric films were taken before and after treatment.Cephalometric analysis was performed.Results After the treatment SNA changed from (79.0±1.2)°to(81.9±0.8)°(P＜0.01).And the inclination of lower incisors was decreased from (25.6±2.1)°to(20.1±1.4)°when measured to the NB line(P＜0.01).The direction of the facial growth was maintained.Conclusions Good orthodontic results could be achieved in patients with skeletal Class Ⅲ malocclusion and open bite.