Objective To observe the effect of resin filling and metal preformed crown on the cosmetic repair effect of root canal therapy for dental caries in children. Methods From January 2022 to December 2023, 80 children with root canal treatment and dental caries repair received by Fengze Street Community Health Service Center, Fengze District, Fujian were selected and divided into control group and observation group by random number table method, with 40 children in each group. The control group was filled with resin, and the observation group was filled with metal preformed crown. The cosmetic repair effect, occlusal function, chewing efficiency, tooth aesthetic satisfaction, complication rate and filling effect were compared between the two groups. Results The total effective rate of cosmetic repair in the observation group was 97.50%, which was higher than 87.50% in the control group (P <0.05). After treatment, the maximum occlusal contact area, bite force and masticatory efficiency of the observation group were higher than those of the control group, the aesthetic satisfaction of teeth was higher than that of the control group, the incidence of complications was lower than that of the control group, and the scores of repair retention, edge tightness and pulp vitality were lower than those of the control group (P<0.05). Conclusion Compared with resin filling, metal preformed crown has a positive effect on the cosmetic repair effect of root canal therapy for dental caries in children, which can improve the total effective rate of cosmetic repair, the satisfaction of dental aesthetics, promote the recovery of occlusal function and masticatory function, and reduce the incidence of complications.