Objective：To study the distance between the upper central incisors and the incisive canal，and further discuss the effect of inclination of upper central incisors on the distance. Methods：A total of 67 adult skeletal Ⅱ and angle Ⅱ orthodontic patients were included in this study. CBCT and Dolphin11.9 software were used to measure the distance between the incisive canal and upper central incisor roots at two planes：the palatal opening level（F1），and the root apex level of the maxillary central incisors（F2）. Then，all patients were divided into three groups（procline，upright，and recline）according to ∠U1-PP. One-way ANOVA or rank sum test was performed for statistical analysis. Results：At F1 and F2 planes，the anteroposterior distance between upper incisor roots and the anterior line of incisive canal（Lml）was（3.27±1.02）mm and（3.07±1.35）mm，respectively. As for three groups，Lc of procline group was significantly lower than upright group and recline group at F1 plane；while Lml of recline group was significantly larger than the other two groups at F2 plane. Conclusion：There is strict limit in tooth movement during retraction of the maxillary incisors in adult skeletal Ⅱ orthodontic patients. The upper incisor roots of procline group were much closer to the incisive canal，while the upper incisor roots of recline group were much far away from the incisive canal.