Background: Diet quality significantly influences aging processes and age-related health outcomes. This study aims to explore the association between dietary quality and accelerated aging in two large cohorts. Methods: This study collected data from the Kailuan and National Health and Nutrition Examination Survey (NHANES) cohorts; participants' dietary quality was evaluated using the American Heart Association (AHA) dietary score and Healthy Eating Index-2015 (HEI-2015), respectively. Accelerated aging in participants was determined by calculating the difference between phenotypic age and chronological age. Logistic regression models were used to explore the association between dietary quality scores and accelerated aging. Additionally, variations in this association across different subgroups were investigated. To minimize the influence of excessive aging, individuals aged 75 and above were excluded in sensitivity analyses. Results: In this study, we included 33 701 participants (27.3% female, mean age 57.29 +/- 11.88) from the Kailuan study and 9285 participants (50.6% female, mean age 49.83 +/- 17.62) from NHANES. In the Kailuan cohort, individuals with dietary scores ranging from 3 to 5 exhibited a 22% lower risk of accelerated aging compared to those scoring between 0 and 2 (OR = 0.78, 95% CI = 0.72-0.85). Similarly, in the NHANES cohort, participants in the highest quartile of HEI-2015 experienced a 34% reduction in the risk of accelerated aging compared to those in the lowest quartile (OR = 0.66, 95% CI = 0.52-0.84). Subgroup analyses underscored a more pronounced association between dietary quality and accelerated aging among males and individuals with unhealthy lifestyles. Sensitivity analyses confirmed the robustness of the association between dietary quality and accelerated aging. Conclusion: In summary, our study found a significant association between dietary quality and accelerated aging. Better dietary quality was associated with a reduced risk of accelerated aging, particularly among males, smokers, and participants with unhealthy lifestyles. Diet quality significantly influences aging processes and age-related health outcomes.