Objective： To investigate the alveolar bone defects of anterior alveolar bone in patients with bimaxillary protrusion by using cone-beam computed tomography (CBCT). Methods: The samples consisted of 50 patients with bimaxillary protrusion, who were assigned to the teenage group［20 cases, （13.1±1.0） years］ and adult group［30 cases, (22.9±4.2) years］ . The adult group included 9 hypo-divergent, 11 normo-divergent and 10 hyperdivergent patients. The images were obtained by using NewTom VG CBCT and the alveolar defects were evaluated. Results: The ratio of the patients had alveolar bone defects was 94.00%. Meanwhile, the defects were associated with 38.60% of all the teeth. Most defects occurred on labial alveolar bone (98.66%); fenestration was found more in the maxillary alveolar region and dehiscence occurred more in the mandible. The dehiscences (3.06%) and defects prevalence (30.13%) of the teenage group were significant lower than those of the adult group (11.73% vs. 42.46%), P<0.05; while there was no significance of the fenestrations prevalence between the two group (P>0.05). The hypo-divergent group had lower fenestrations prevalence (22.22%) than the normo-divergent (33.84%) and hyper-divergent groups (37.50%), P<0.05. The upper central incisor had the lowest alveolar bone defect prevalence. Conclusion: Alveolar bone defects are common findings in patients with bimaxillary protrusion before orthodontic treatment. The prevalence of defects is affected by age and vertical-growth type.