Background: The effect of dietary antioxidant capacity on health has attracted increasing attention, but unequivocal evidence for its benefits on cardiovascular diseases is still lacking. Objectives: Our aim was to assess the association between composite dietary antioxidant index (CDAI) and Life's Essential 8 (LE8), an evaluation indicator of cardiovascular health (CVH), in two large cohorts. Methods: The cross-sectional study used data from the National Health and Nutrition Examination Survey (NHANES) 2005-2018 and Community Cohort Study on Specialized Nervous System Diseases (CCSNSD) 2018. The relationship between CDAI and CVH was studied by multinomial logistic regression, restricted cubic spline, subgroup and sensitivity analysis. Results: After adjusting for all potential confounding factors, it suggested that higher CDAI was positively associated with higher CVH (NHANES: OR Q4 vs. Q1 = 0.19, 95% CI: 0.14-0.25; CCSNSD: OR Q4 vs. Q1 = 0.03, 95 % CI: 0.03-0.04). And a nonlinear dose-response relationship between CDAI and CVH was observed in two large cohorts. The robustness of the results was further demonstrated by sensitivity analysis. Among them, Mendelian randomization analysis showed that higher Vitamin C and Vitamin E intakes were causally associated with a lower risk of CVD. Moreover, there was a stronger positive correlation between the CDAI and CVH among individuals with lower socioeconomic status in both cohorts. Conclusion: Our findings demonstrated the potential benefit of dietary antioxidant intake in improving CVH. Besides, the relationship between CDAI and CVH may be influenced by income levels, highlighting the need for targeted interventions in populations with low income to increase CVH levels.