Objective To explore the effect of Nolla staging on the inclination angle of mandibular third molars in adolescent orthodontic patients undergoing tooth extraction. Methods A total of 100 adolescent patients who underwent tooth extraction orthodontic treatment from October 2018 to October 2022 were included．All 100 patients had 4 premolars extracted,with a total of 100 mandibular third molars．According to Nolla staging,the 100 patients can be divided into 4 groups,with 25 cases in each group．Group I：The crown was forming,Group II：The crown was basically formed,Group III：The root formation was below 1/2,Group IV：The root formation was above 1/2．The inclination angle of the mandibular third molar was measured before and after treatment,and the angle α changes will be analyzed. Results There was no difference in the inclination angle,MP-SN,and MP-FH of the third molar tooth germ among different groups（F=0.256,P=0.857;F=0.033,P=0.992;F=0.028,P=0.994）．There was no difference in the angle of mandibular third molar teeth between groups before treatment（P>0.05）,the contrast of mandibular third molar angles between different groups after treatment was signifiant（F=13.376,P<0.001）,while the angles in Group I,Group and Group Ⅳ were not slgnificantly different（t=0.757,P=0.453;t=0.224,P=0.824;t=0.852,P=0.399）,and the angle change decreased after treatment in Group Ⅲ（t=3.697,P<0.001）. Conclusions After orthodontic extraction in adolescents,if the mandibular third molar is less than half of the root formation stage,it may lead to increased mesial inclination of the third molar．However,when the mandibular third molar is in the stage of crown formation and the crown is more than half formed,the angle change of the third molar is relatively small．Therefore,in clinical practice,Nolla staging should be evaluated in the prognosis of mandibular third molars before treatment and develop corresponding intervention strategies in a timely manner．