Objective To explore the effect of metal preformed crown restoration on masticatory function in children with primary molar tooth defect. Methods A total of 120 children with primary molar tooth defect admitted to Nanchong Hospital, Beijing Anzhen Hospital Afffliated to Capital Medical University·Nanchong Central Hospital from January 2024 to June 2025 were selected as the research subjects, and they were divided into the reference group and the experimental group by the random number table method, with 60 children in each group. The reference group received conventional resin fflling restoration, and the experimental group received metal preformed crown restoration. The masticatory function, aesthetic effect, restoration success rate, parental satisfaction rate and complication rate were compared between the two groups. Results The maximum occlusal area, maximum occlusal force and masticatory efffciency in the experimental group after restoration were better than those in the reference group (P<0.05). The scores of PES and WES in the experimental group after restoration were higher than those in the reference group (P<0.05). The restoration success rate of the experimental group was 98.33%, which was higher than 88.33% of the reference group (P<0.05). The parental satisfaction rate of the experimental group (98.33%) was higher than that of the reference group (86.67%) (P<0.05). The incidence of complications in the experimental group (1.67%) was lower than that in the reference group (11.67%) (P<0.05). Conclusion Metal preformed crown restoration for children with primary molar tooth defect can effectively restore the masticatory function of affected teeth, and has advantages in aesthetic effect, restoration success rate and parental satisfaction, with a lower incidence of complications.