Objective: To evaluate the diagnostic accuracy of cone beam computed tomography (CBCT) with different resolution settings in detecting the simulated external root resorption defects. Methods: External root resorption defects were simulated in 51 human single rooted premolar teeth. Ca-vities simulating root resorption defects of 1 mm in diameter and 0.1 mm, 0.2 mm, and 0.3 mm in depth were drilled in the cervical, middle and apical thirds of lingual surfaces of the teeth. In addition to the 51 locations as controls, a total of 102 cavities were obtained in the present study. Specimens were placed in a human dry mandible and scanned by ProMax 3D and DCT PRO CBCT with different resolution settings, respectively. The three-dimensional CBCT images were evaluated by two experienced observers. The data were analyzed with receiver operating characteristics (ROC) analysis. ROC curves were generated and the area under ROC curve (Az) was employed to express the diagnostic accuracy. Results: The diagnostic accuracy (Az value) of ProMax 3D CBCT with high, normal and low resolution settings were 0.867, 0.703 and 0.665 (P < 0.05), respectively. Defects with depths of 0.2 mm and 0.3 mm were easier to be detected than those with depths of 0.1 mm (P < 0.05). The images obtained by high resolution mode scanning had obvious advantages in detecting smaller defects (depth 0.1 mm and 0.2 mm). The DCT PRO CBCT provided 4 resolution settings including normal quality + normal resolution, normal quality + high resolution, high quality + normal resolution and high quality + high resolution. The Az values for those 4 resolution settings were 0.527, 0.725, 0.743, and 0.794 (P < 0.05), respectively. Similar to ProMax 3D CBCT, the scanning mode with high resolution played a better role in detecting the defects with depth of 0.1 mm. Except for the scanning setting mode with normal quality + normal resolution, the other three modes could well be evaluated for the defects with depth of 0.2 mm and 0.3 mm. Conclusion: It is concluded that the diagnostic ability for external root resorption of CBCT could be affected by resolution settings. Computer-aid imaging method can improve the CBCT diagnostic accuracy for external root resorption without increasing the radiation dose level during CBCT scanning.