Objective To explore the clinical effect of metal prefabricated crown in repairing large area defect of deciduous molars in children. Methods A total of 92 children with large area defect of deciduous molars admitted to Guilin Stomatological Hospital from January 2020 to September 2022 were selected as the research objects. They were divided into control group and experimental group by random number table method, with 46 children in each group. The control group was treated with solidified resin restoration, and the experimental group was treated with metal prefabricated crown restoration. The periodontal indexes, aesthetic satisfaction, clinical efficacy and complications were compared between the two groups. Results After treatment, the gingival index and plaque index of the experimental group were lower than those of the control group, and the differences were statistically significant (P <0.05). After treatment, the aesthetic satisfaction score of the experimental group was higher than that of the control group, and the difference was statistically significant (P<0.05). The total effective rate of treatment in the experimental group was 97.83%, which was higher than 82.61% in the control group, and the difference was statistically significant (P <0.05). The incidence of complications in experimental group was 4.35%, which was lower than 21.74% in control group, and the difference was statistically significant (P <0.05). Conclusion The clinical effect of metal prefabricated crown in repairing large area defect of deciduous molars in children is good, which can effectively improve the periodontal index of children, improve the aesthetic satisfaction and repair effect of teeth, and the risk of complications after repair is low and the safety is high.