Background Atrial fibrillation (AF) is the most common persistent cardiac arrhythmia. This study aimed to estimate its prevalence and explore associated factors in adults aged 18 years or older in China. Methods Study data were derived from a national sample from July 2020 to September 2021. Participants were recruited using a multistage stratified sampling method from twenty-two provinces, autonomous regions, and municipalities in China. AF was determined based on a history of diagnosed AF or electrocardiogram results. Findings A total of 114,039 respondents were included in the final analysis with a mean age of 55 years (standard deviation 17), 52.1% of whom were women. The crude prevalence of AF was 2.3% (95% confidence interval [CI] 1.7-2.8) and increased with age. The age-standardized AF prevalence was 1.6% (95% CI 1.6-1.7%) overall, and 1.7% (1.6-1.8%), 1.4% (1.3-1.5%), 1.6% (95% CI 1.5-1.7%), and 1.7% (1.6-1.9%) in men, women, urban areas, and rural areas, respectively. The prevalence was higher in the central regions (2.5%, 2.3-2.7%) than in the western regions (1.5%, 1.0-2.0%) and eastern regions (1.1%, 1.0-1.2%) in the overall population, either in the gender or residency subgroups. The associated factors for AF included age (per 10 years; odds ratio 1.41 [95% CI 1.38-1.46]; p < 0.001), men (1.34 [1.24-1.45]; p < 0.001), hypertension (1.22 [1.12-1.33]; p < 0.001), coronary heart disease (1.44 [1.28-1.62]; p < 0.001), chronic heart failure (3.70 [3.22-4.26]; p < 0.001), valvular heart disease (2.13 [1.72-2.63]; p < 0.001), and transient ischaemic attack/stroke (1.22 [1.04-1.43]; p = 0.013). Interpretation The prevalence of AF was 1.6% in the Chinese adult population and increased with age, with significant geographic variation. Older age, male sex, and cardiovascular disease were potent factors associated with AF. It is crucial to increase the awareness of AF and disseminate standardized treatment in clinical settings to reduce the disease burden. Copyright (c) 2022 Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license (http:// creativecommons.org/licenses/by-nc-nd/4.0/)