Objective: To explore the influence of birth weight and growth patterns during infancy on overweight and obesity among first grade primary school pupils, so as to provide a theoretical basis for the formulation of early life prevention and intervention policies. Methods: In 2019, data related to routine physical examinations were collected for primary school pupils in the Minhang District of Shanghai, and information regarding birth and follow ups was collected retrospectively. Physical examination data of 4 434 pupils at 12 months of age were obtained. A multiple linear regression model was used to analyze the relationship between growth patterns during infancy and body mass index (BMI) in the first grade of primary school. A generalized linear model was employed to analyze the relationship between birth weight and growth patterns during infancy and overweight and obesity in the first grade of primary school. A hierarchical analysis was conducted. Results: A linear relationship was observed between growth patterns during infancy and BMI and the BMI Z score of first grade primary school pupils [ β(β 95%CI)=0.30(0.24-0.35),0.12(0.10- 0.15 ), P <0.01]. In addition to subjects classified as small for gestational age (SGA), catch up growth during infancy was identified among subjects who were classified as appropriate for gestational age (AGA) and large for gestational age (LGA). LGA at birth and catch up growth during infancy were independent risk factors for overweight and obesity among first grade primary school children ( RR =1.31-1.55, P <0.05). The hierarchical analysis showed that catch up growth increased the risk of overweight and obesity among first grade primary school pupils classified as AGA [ RR(RR 95%CI )=1.74(1.42-2.14),1.87(1.56-2.26)], and increased the risk of obesity among first grade primary school pupils classified as SGA and LGA [ RR(RR 95%CI )=3.74(1.04-13.49),3.24(1.62-6.46)]( P <0.05). Among those who exhibited catch up growth during infancy, LGA increased the risk of obesity among first grade primary school pupils ( RR= 2.60 , 95%CI=1.35-5.02, P <0.01), but not the risk of being overweight ( P =0.13). Conclusion Birth weight and growth patterns during infancy have an impact on overweight and obesity among children in the first grade of primary school. It is suggested that attention should be paid to growth and physical development in early life for those classified as LGA and AGA, and catch up growth in children should be closely monitored.