Objective To explore the effect of corticotomy-assisted orthodontics (CAO) combined with segmental arch technique on tooth position stability and root resorption in patients with elongated molars. Methods A total of 102 patients with unilateral elongated molars who were treated in the Department of Orthodontics, Lanzhou Stomatology Hospital from January 2022 to March 2023 were selected as the research subjects, and they were divided into the control group and the experimental group by the random number table method, with 51 patients in each group. The control group received segmental arch technique treatment, and the experimental group received CAO combined with segmental arch technique treatment. The tooth position stability, root resorption, treatment efficiency indicators, periodontal health indicators and masticatory function were compared between the two groups. Results The vertical recurrence amounts of the experimental group at 3, 6 and 12 months after treatment were lower than those of the control group (P <0.05). The incidence of root resorption in the experimental group was 11.76%, which was lower than 27.45% in the control group (P <0.05). The total treatment time, tooth movement rate and number of follow-up visits in the experimental group were better than those in the control group (P <0.05). There were no significant differences in PD, CAL and BI between the two groups (P >0.05). The masticatory function score of the two groups at 12 months after treatment was higher than that before treatment (P <0.05), but there was no significant difference in masticatory function score between the two groups at 12 months after treatment (P >0.05). Conclusion CAO combined with segmental arch technique can improve molar intrusion efficiency, reduce the risk of root resorption, and enhance long-term stability, which is an effective method for clinical treatment of elongated molars.