Objective To investigate the prevalence of alveolar dehiscence and fenestration in patients with skeletal Class Ⅲ malocclusion at different tooth sites,gender and cervical vertebral maturation by using cone beam CT(CBCT). Methods The samples included 78 patients with skeletal Class Ⅲ malocclusion,who visited the Second Department of Orthodontics and the First Dental Clinic,Hospital of Stomatology,China Medical University from 2018 to 2021. The patients were evaluated their cervical vertebral maturation by radiographic cephalometric projection through cephalometer and cervical vertebrae maturation system. Then three-dimensional CBCT reconstruction was performed and the images were analyzed to investigate the prevalence of alveolar dehiscence and fenestration at different tooth sites,gender and cervical vertebral maturation. Results Totally 72 patients(92.31%,72/78)had alveolar bone defects,among which the prevalence of dehiscence was 92.31%(72/78),and the prevalence of fenestration was 11.54%(9/78). The alveolar bone defects occurred in 502 teeth(24.44%,502/2054),among which 489 teeth(97.41%,489/502)had dehiscence,and 13 teeth(2.59%,13/502)had fenestration. The prevalence of alveolar dehiscence in mandible was higher than that in maxilla,and the difference was statistically significant(χ2 = 24.515,P < 0.001). There were statistically significant differences in the prevalence of dehiscence and fenestration at different tooth sites(P < 0.01). The prevalence of alveolar dehiscence in male patients was higher than that in female patients,and the difference was statistically significant(χ2 = 5.463,P = 0.019). Further analysis of patients with the same gender was made according to different cervical vetebral maturation,which showed that the prevalence of alveolar dehiscence in male and female patients at different cervical bone vetebral maturation had statistically significant difference(all P < 0.01). Conclusion Alveolar dehiscence and fenestration are common in patients with skeletal Class Ⅲ malocclusion before orthodontic treatment,and the prevalence is related to tooth site,gender,cervical vetebral maturation and other factors.