〔Abstract〕 Objective To evaluate the effect of modified vertical tooth preparation with full zirconium crown restoration in molar area. Methods A randomized study was conducted in 84 patients with all-ceramic crown restoration of posterior teeth. 90 full crown restorations were collected and randomly divided into two groups: 45 teeth in experimental group were treated with modified vertical tooth preparation, while 45 teeth in control group were treated with conventional horizontal tooth preparation with full zirconium crown restoration. When patients wore teeth, the restoration effects of the two groups were evaluated respectively, and then the marginal and internal fitness of the two groups were measured by silicone rubber replication method; gingival index(GI) and sulcus bleeding index(SBI) scores were recorded 6 months after wearing teeth. Results The results of chair-side evaluation of the two groups showed that the marginal fitness of the experimental group was better than that of the control group, and the difference was statistically significant(P=0.036); the measured value of marginal fitness of prostheses in experimental group was better than that in control group, and the difference was statistically significant(P<0.001); after 6 months, there was no mechanical complication between the two groups, and there was no significant difference in GI and SBI scores of periodontal soft tissue indexes. Conclusion Modified vertical tooth preparation abutment can significantly improve the marginal fitness of all-ceramic crown, which will not change the health status of peri-crown gingiva.