Objective To compare the effects of deep margine elevation and crown lengthening surgery in the restoration of subgingival defects with all-ceramic high onlay. Methods From January to December 2023, 120 patients with posterior dental defect who underwent all-ceramic high onlay restoration in the Department of Stomatology, Panyu Eighth People's Hospital were selected as the research subjects, and they were divided into control group and observation group by the random number table method, with 60 patients in each group. The control group was treated with crown lengthening surgery+all-ceramic high onlay restoration, and the observation group was treated with deep margine elevation+all-ceramic high onlay restoration. The restoration success rate, restoration satisfaction and oral health-related quality of life were compared between the two groups. Results There was no significant difference in the success rate of restoration fracture, restoration loss, gingival index, edge tightness, color matching and secondary caries between the two groups (P >0.05). The satisfaction of restoration time and times in the observation group was higher than that in the control group (P <0.05). There was no significant difference in the satisfaction of restoration shape, restoration color and restoration comfort between the two groups (P >0.05). The OHIP score of the two groups at 3 months after treatment was lower than that before treatment, and that in the observation group was lower than the control group (P <0.05). Conclusion The effects of deep margine elevation and crown lengthening surgery in the restoration of subgingival defects with allceramic high onlay are better, and the restoration success rate and restoration satisfaction are higher, but deep margine elevation has less traumatic injury and is more conducive to maintaining oral health status, thus promoting the improvement of related quality of life. The surgical method should be reasonably selected according to the actual situation.