Background <p>The effects of prenatal exposure to fine particulate matter (PM_2.5) on fetal birth weight (FBW) results have been inconsistent, and the crucial components of PM_2.5 may be responsible for these harmful effects. We aimed to explore the effects of prenatal exposure to PM_2.5 components on FBW and determine the pregnancy susceptible exposure windows for PM_2.5 components.</p> Methods <p>We analyzed data from a birth cohort of 10,164 mother-infant pairs in Hefei, China. The study included singleton live births delivered between 2017 and 2021, with complete exposure and covariate data. We assessed pregnancy exposure to PM_2.5 and its components (NH₄⁺: ammonium; NO₃⁻: nitrate; SO₄²⁻: sulfate; OM: organic matter; BC: black carbon) with spatial datasets matched to participants’ residential addresses, and assessed green space using the Normalized Difference Vegetation Index (NDVI). Generalized linear regression assessed the crucial components of PM_2.5 affecting FBW Z-scores, and to further explore the susceptibility windows. Stratified analyses were conducted to explore potential moderating effects of green space.</p> Results <p>Our study found that pregnancy exposure to PM_2.5 and its components was associated with reduced FBW Z-scores, with black carbon (BC) having a stronger negative effect. Each 1&#xa0;µg/m³ increase in BC was associated with an expected FBW Z-score decrease of β&amp;95%CI: -0.1176 (-0.1791, -0.0560). The most crucial periods for the effect of PM_2.5 components on FBW Z-scores were the second and third trimesters. Finally, we observed that higher levels of green space exposure showed a protective effect on FBW Z-scores.</p> Conclusions <p>Our research highlights that certain PM_2.5 components like BC impact FBW negatively, particularly in the second and third trimesters, and that green space can mitigate this negative effect. This study provides scientific evidence for PM_2.5 emission source control and maternal and child health protection.</p>