Abstract: Objective To analyze the effects of preterm birth and low birth weight on infant development, and to explore the potential interaction effect of preterm birth and low birth weight on the development of infants. Methods Data of infants at the age of 8 to 10 months receiving Denver Development Screening Test (DDST) from September 2013 to December 2017 in Tongzhou District of Beijing City were collected through the electronic information system of Maternal and Child Health Care Hospital of Tongzhou District. Using the method of nested case-control study, the children with DDST screening results of "suspicious" or "abnormal" were taken as the case group, and the children with DDST screening results of "normal" were taken as the control group. Chi-square test was used to analyze the development of infants and its influencing factors. Univariate and multivariate unconditional logistic regression models were used to analyze the possible influence of preterm birth and low birth weight on infant development. The interaction effect of preterm birth and low birth weight on infant development was investigated by using the additive and multiplicative interaction models. Results A total of 22 455 infants aged from 8 to 10 months were included in this study and the prevalence of suspicious/abnormal DDST results was 2.6%. The infant with younger gestational age or lower birth weight might have higher risk of suspicious/abnormal DDST results at the age of 8 to 10 months. In interaction analysis, preterm birth and low birth weight were observed to have additive interaction to the infant development (RERI=2.55, 95%CI: 0.54-4.55), but their multiplicative interaction was not observed (OR=1.50，95%CI：0.68-3.30). Conclusion There was an additive interaction between preterm birth and low birth weight, and no multiplicative interaction was found between these two factors. It should be paid more attention on the early development of infants with preterm birth and low birth weight.