Objective To compare the effects of Twin-Block and Activator on upper airway structure in skeletal class Ⅱ adolescents. Methods A total of 68 patients with skeletal class Ⅱ adolescents admitted to our hospital from December 2020 to December 2021 were selected as the research objects. They were divided into control group and observation group by random number table method, with 34 cases in each group. The control group wore Twin-Block appliance, and the study group wore Activator appliance. The upper airway soft and hard palate, retrolingual airway indexes and upper airway sagittal diameter indexes were compared between the two groups. Results After treatment, Ve1-Ve2, P1-P2 and Pas1-Pas2 in the two groups were higher than those before treatment, and those in the study group were higher than those in the control group (P<0.05). There was no significant difference in PNS-S, PNS-Aa, PNS-Ad1 and PNS-Ad2 between the two groups (P>0.05). Conclusion Both Twin Block and Activator appliance can effectively improve skeletal class Ⅱ adolescents' upper airway structure and improve the respiratory ventilation efficiency. However, Activator appliance has a better effect on the sagittal diameter of velopharyngeal and glossopharyngeal segments, and the appliance can be reasonably selected according to the actual situation of patients.