Background There is a global increase in the prevalence of autism spectrum disorder (ASD). Early identification of ASD in children and intervention are key aspects in the management of ASD. However, early identification is partly dependent on knowledge on ASD among pediatricians. This study analyzed the extent of ASD knowledge and its underlying factors among pediatric residents in eastern China, to provide a reference for medical education reforms. Methods The study employed the Knowledge about Childhood Autism among Health Workers questionnaire. A total of 138 pediatric residents participated in the survey. Descriptive statistics were used to describe demographic characteristics and the four domains of the questionnaire. Univariate analysis was employed to assess impacts of the demographic characteristics on the questionnaire scores. On the other hand, multivariate regression analysis was used to analyze the correlation between the participants' demographic characteristics and the questionnaire scores. Results The average ASD cognitive score of 138 respondents was 13.38 +/- 4.48. The ASD cognitive scores in female pediatric residents were higher compared to that in males (p < 0.05). Residents who had obtained professional doctor qualification certificate were more than those without professional doctor qualification certificate (p < 0.05). The ASD knowledge in the group which did not have rotation in both departments was lower than in the group which had rotation in both departments (p < 0.05) as well as the group that had rotation in developmental and behavioral pediatrics department only (p < 0.05). Our multivariate linear regression model demonstrated significant statistical differences (p < 0.05), and showed that gender and systematic exposure to ASD knowledge had significant effects on cognitive scores (p < 0.05). Conclusion Most participants had relatively low levels of awareness and knowledge about ASD, especially on ASD comorbidities and age of onset. Women, systematic learning of ASD knowledge in medical school, successful passing of the physician examination, and rotation in the developmental and behavioral pediatrics (DBP) department significantly influence the levels of ASD awareness and knowledge. It is, therefore, important to strengthen ASD education in medical students at the university level and make rotation in the DBP department a requisite for pediatric trainees.