Purpose <p>To investigate the impact of secondhand smoke (SHS) exposure on myopia prevalence and risk among nonmyopic children in China.</p> Methods <p>This was a retrospective cohort study. A total of 232 children aged 5–10 years were included, with 128 exposed to SHS and 104 who were not. Baseline characteristics such as age, sex, height, weight, spherical equivalent refraction (SER), axial length (AL), average corneal K-reading (Ave-K), intraocular pressure (IOP), pupil diameter (PD) and subfoveal choroidal thickness (SFCT) were measured. Follow-up assessments at 3-, 6-, 9-, and 12-month visits were focused on changes in SER and AL. Behavioural and parental factors, including parental myopia status, parental education level, daily time spent on near work and outdoor activities were collected via questionnaires from medical records. Linear regression was applied to identify the factors that have a significant impact on axial elongation over 1 year.</p> Results <p>The mean spherical refraction myopic shift in the SHS group was − 0.64 ± 0.41 D/year, which was significantly greater than that in the control group (-0.47 ± 0.52 D/year) (<i>P</i> = 0.004). Children in the SHS group had significantly greater axial elongation than did children in the control group (0.26 ± 0.14&#xa0;mm vs. 0.20 ± 0.13&#xa0;mm, <i>P</i> = 0.002). Multivariate linear regression analysis revealed that SHS exposure (β = 0.053, <i>P</i> = 0.002), baseline SER (β = -0.054, <i>P</i> = 0.001) and parental myopia (β = 0.028, <i>P</i> = 0.036) were significant predictors of 12-month axial elongation.</p> Conclusions <p>This retrospective cohort study revealed that SHS exposure was associated with a greater likelihood of developing early-onset myopia. These findings indicate that eradicating SHS exposure is highly important for preventing myopia among children, especially in families with young children.</p>