Objective: To examine the association between secondhand smoke exposure (SHS) in indoor public places and carotid intima media thickness (cIMT) in children and adolescents, so as to provide guidance for the prevention of early abnormal vascular architecture. Methods: The data were obtained from the second follow up of the Children Cardiovascular Health Cohort Study conducted from November to December 2021. A total of 1 297 children and adolescents for who completed data relating to sex, age, cIMT, physical examinations, questionnaires variables and blood biochemical indices, were included for analysis. Linear regression analysis was performed to examine trends in the levels of cIMT with exposure to SHS in indoor public places. Multiple linear regression analysis was carried out to assess the association between SHS exposure in indoor public places and cIMT after adjustment for potential covariates. Results: During the previous 7 days, 407 (31.4%) children and adolescents were exposed to SHS in indoor public places for 1-2 days, 86 (6.6%) for 3-4 days, and 82 (6.3%) for ≥5 days. The levels of cIMT in youth increased on different models, with the duration of SHS exposure during the previous 7 days ( t=3.30, 3.05, 2.87, P <0.05). After adjusting for various covariates, the cIMT values of children and adolescents were[0 day:(551.5±29.3) μm, 1-2 days:(554.0±28.6) μm, 3-4 days:(557.0±27.7) μm, ≥5 days:(559.4±27.5) μm]. Compared to those who were not exposed to SHS in indoor public places during the previous 7 days, those exposed for ≥5 days had significantly higher cIMT levels ( β=7.91, 95%CI=1.47-14.34, P <0.05). Conclusion Among children and adolescents, exposure to SHS in indoor public places remains high and is significantly associated with cIMT. The findings highlight the need for stricter regulation and tobacco control policies to provide healthy smoke free environments for children and adolescents, and to reduce the risk of early abnormal vascular architecture.