To analyze the risk factors for the failure of CAD/CAM system-designed all-ceramic onlays in repairing dental defects using the nomogram model.Clinical data from 236 patients with dental defects in Yulin First Hospital from January 2019 to January 2021 was conducted. All patients received all-ceramic onlay restorations designed by CAD/CAM system and were followed up for 3 years. According to the follow-up results, they were divided into successful group(n=169) and failed group(n=67). Basic details were collected for each group, including gender, age, smoking history, tooth type, type of tooth defect, dental arch defect status, root canal treatment status, type of ceramic block, measurements of pre-treatment occlusal force, alveolar bone density and periodontal indices [plaque index (PLI), sulcus bleeding index(SBI) and probing depth(PD)]. Logistic regression analysis was used to identify the risk factors for failure after all-ceramic onlay restoration, the prediction model of nomogram was constructed and the fitting effect of the model was evaluated.Logistic regression analysis indicated that older age, comorbid diabetes, smoking history, molar teeth, use of CEREC Blocs ceramic, multi-surface cavity defects, incomplete dental arch post-restoration, high pre-treatment occlusal force, low alveolar bone density, high values of PLI, SBI and PD were related to an increased likelihood of treatment failure(P＜0.05). The calibration curve for this predictive model approximates the ideal curve.Age, history of diabetes, smoking history, condition of the defective tooth and periodontal health status are significant factors influencing the failure of CAD/CAM system-designed all-ceramic onlay restorations for dental defects.