Objective To investigate the difference in the effect of composite resin restoration and metal preformed crown restoration in children with interproximal caries of primary molar. Methods A total of 120 children with interproximal caries of primary molar admitted to our hospital from February 2022 to May 2023 were selected as the research objects. The children were divided into conventional group and experimental group by random number table method, with 60 children in each group. The conventional group was treated with composite resin filling for restoration. The experimental group was treated with metal preformed crown for restoration. The treatment effect, occlusal function, satisfaction and complication rate were compared between the two groups. Results The total effective rate of treatment in the experimental group was 98.33%, which was higher than 85.00% in the conventional group (P <0.05). After treatment, the maximum bite force and masticatory efficiency of the experimental group were higher than those of the conventional group (P <0.05). The satisfaction rate of treatment effect in the experimental group was 98.33%, which was higher than 83.33% in the conventional group (P <0.05). The incidence of complications in the experimental group was 1.67%, which was lower than 10.00% in the conventional group (P <0.05). Conclusion The clinical effect of metal preformed crown in the treatment of interproximal caries of primary molar is good, which can improve the occlusal function of children, reduce the incidence of complications, and has high satisfaction with treatment.