BackgroundHigh particulate matter with an aerodynamic diameter of 2.5 μm or less (PM2.5) exposure levels posed a great risk to human health, but the protection effects of environmental protection on cardiovascular disease have not been systematically evaluated. This study aims to illustrate the effect of the decreased concentration of PM2.5 on blood pressure level in adolescents after enacting the protection measures of environment from a cohort study.MethodsA quasi-experimental study including 2415 children from the Chongqing Children’s Health Cohort, aged 7.32 ± 0.60 years with normal blood pressure at baseline, with 53.94% males, were analysed. Both the generalised linear regression model (GLM) and Poisson regression model were used to calculate the impact of the declining exposure level of PM2.5 on blood pressure and the incidence of prehypertension and hypertension.ResultsThe annual mean PM2.5 concentration in 2014 and in 2019 were 65.01 ± 6.46 µgmes per cubic metre (μg / m3), 42.08 ± 2.04 μg / m3respectively, and the decreased PM2.5 concentration between 2014 and 2019 was 22.92 ± 4.51 μg / m3. The effect of decreased PM2.5 concentration by 1μg / m3on systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP) and the difference of blood pressure (BP) indexes between 2014 and 2019 were all significant (P< 0.001). The absolute differences of SBP (-3.598 mmHg; 95% confidence interval (CI) = -4.47,-2.72 mm Hg), DBP (-2.052 mmHg; 95% CI = -2.80,-1.31 mm Hg) and MAP (-2.568 mmHg; 95% CI = -3.27,-1.87 mm Hg) in the group with a decreased level of ≥25.56 μg / m3were more significant than those in a decreased concentration of PM2.5 for <25.56 μg / m3(P< 0.001). And the incidence of prehypertension and hypertension for three occasions blood pressure diagnose was 2.21% (95% CI = 1.37%-3.05%,P= 0.001) in children with PM2.5 decreased level ≤25.56 μg / m3(50%), which was significant higher than its’ counterparts 0.89% (95% CI = 0.37%-1.42%,P= 0.001).ConclusionsOur study found the etiological relationship between the declining PM2.5 concentration and the BPvalues and the incidence of prehypertension and hypertension in children and adolescents, suggesting continuous environmental protection measures in China have achieved remarkable health benefits.