Abstract: [Abstract] Objective: To study the related risk factors of state change of mandibular third molar in orthodontic treatment. Methods: 298 patients with orthodontic treatment in the department of stomatology in our hospital from January 2014 to December 2016 were divided into the vertical eruption group (n=250 cases) and the state change group (n=93 cases). The related factors of affecting the change of mandibular third molar after orthodontic treatment was statistical analyzed. Results: The age of mandibular third molar, mandibular plane angle, anteversion angle before treatment and the ratio of gap / width before treatment in the vertical eruption group were significantly lower than those of the state group (P < 0.05). However, there was no significant difference in age, treatment time, age at the beginning of orthodontic treatment and cervical development stage between the two groups (P > 0.05). Univariate analysis and logistic analysis of mandibular plane angle ≥37.5o, forward angle ≥30o before treatment, the width / space ratio≥0.3 were carried out and non extraction treatment was a risk factor for the change of mandibular third molar after orthodontic treatment (P < 0.05). The age of joining the group, sex, age of starting orthodontic, the tooth age of mandibular third molar and the development stage of cervical spine were not the risk factors of the state change of mandibular third molar after orthodontic treatment (P > 0.05). Conclusion: During orthodontic treatment, mandibular plane angle, anteversion angle and clearance / width of mandibular third molar and whether to pull out the tooth will cause?the mandibular third molar state? unable to sprout or tilt normally. So it is necessary to strengthen the monitoring and evaluation of influencing factors, so as to facilitate timely and effective interventions to improve the therapeutic effect.