BACKGROUND: Atrial fibrillation (AF)/atrial flutter (AFL) are among the most prevalent cardiovascular diseases in the young. This study aimed to assess modifiable risk factors by integrating a global data analysis with a local cohort study. METHODS: Age-standardized rates of AF/AFL prevalence (ASPR), incidence (ASIR), mortality (ASDR), and DALYs, EAPCs were analyzed by regions from 1990 to 2021. In the cohort study, multivariable logistic regression analysis was performed to evaluate the association between risk factors and the odds of atrial arrythmia. Restricted cubic splines (RCS) were used to explore potential non-linear relationships between risk factors and the odds of atrial arrhythmia. RESULTS: A rising global burden of AF/AFL was observed among individuals aged 15 to 39 years. High-SDI areas had the highest AF/AFL-related ASPR, ASIR, and DALYs. Global data identified hypertension, high BMI, smoking, and alcohol consumption as the main modifiable risk factors for AF/AFL, among which hypertension contributes the most. In the cohort study, segmented regression identified significant breakpoints for DBP at 88.3 mmHg and BMI at 28.8 kg/m2, while SBP was positively associated with AF above an estimated value of 117.0 mmHg without a statistically significant slope-change test. Bayesian age-period-cohort (BAPC) analysis projected a modest decline in AF/AFL burden among the young over the next 3 decades. CONCLUSION: The global burden of AF/AFL in the young adult population has increased over the past 30 years. High blood pressure, high BMI, smoking, and alcohol consumption are key modifiable contributors to the increased AF/AFL burden in young adults. Enhanced awareness, targeted screening, and proactive clinical management of these risk factors are critical for mitigating the AF/AFL burden in this demographic.