Objective To observe the clinical effect of prefabricated stainless steel crown in the repair of interproximal caries of primary molar in children. Methods A total of 100 children (150 primary molars) admitted to our hospital from January 2018 to December 2020 were randomly divided into experimental group and control group. The experimental group was repaired with prefabricated stainless steel crown, while the control group was repaired with traditional resin filling. The clinical efficacy and repair effect of the two groups were compared. Results There was no significant difference in the total effective rate between the two groups after 0.5 years of treatment (P>0.05). The total effective rate of the experimental group was higher than that of the control group at 1, 1.5 and 2 years after treatment (P<0.05). The restoration condition, edge tightness, secondary caries, wear and adjacency relationship of the experimental group were better than those of the control group (P<0.05). Conclusion Prefabricated stainless steel crown has a better effect in repairing interproximal caries of primary molar in children. It has better long-term efficacy and can effectively improve the wear of deciduous molars in children.