Objective To explore the effect of preformed metal crown for primary teeth combined with vital pulpotomy on the repair success rate of primary molar defect. Methods A total of 82 children with primary molar defect (82 affected teeth) treated in our hospital from January 2024 to November 2025 were selected, and they were divided into the control group and the observation group by the random number table method, with 41 children in each group. Both groups underwent vital pulpotomy. The control group was repaired with traditional resin fflling, and the observation group was repaired with preformed metal crown. The repair success rate, masticatory function, repair satisfaction and aesthetic effect were compared between the two groups. Results The success rate of repair in the observation group (95.12%) was higher than that in the control group (78.05%) (P<0.05). At 6 months after treatment, the masticatory efffciency of the observation group was higher than that of the control group (P<0.05). The repair satisfaction score of the observation group was (95.14±2.03)points, which was higher than (84.26±3.97)points of the control group (P<0.05). The aesthetic effect score of the observation group was (94.98±3.05)points, which was higher than (85.42±4.04)points of the control group (P<0.05). Conclusion Preformed metal crown for primary teeth combined with vital pulpotomy can effectively improve the repair success rate of primary molar defect, improve masticatory function and repair satisfaction, and have a good aesthetic effect. This restoration method has reliable clinical effects in pediatric dental treatment.