AimThe objective of this study is to evaluate the mean body mass index (BMI), general obesity and abdominal obesity in adults aged >= 40 years residing in China in 2020, and to analyse variations in these factors across different geographic areas and subpopulations.MethodsWe utilized data from the National Stroke High-Risk Population Screening programme to calculate and compare the mean BMI and prevalence of obesity across various demographics, including sex, age, urban-rural locality, geographical region (province) and ethnicity status.ResultsIn our study, we found that the standardized mean BMI level was 24.65 kg/m2 [95% confidence interval (CI): 24.50-22.84] in men and 24.31 kg/m2 (95% CI: 24.15-24.45) in women. Using the criteria from China, we found that the standardized prevalence of general obesity and abdominal obesity was 13.13% (95% CI: 13.05-13.21%) and 33.03% (95 CI: 32.92-33.14%), respectively. Our study also identified significant effects of age, sex, urban-rural locality, province and ethnicity status on the prevalence of obesity. Overall, our study estimated that in 2020, approximately 91.1 million adults aged >= 40 years in China were obese (46.5 million men and 44.6 million women), while 229.2 million adults (110.4 million men and 118.8 million women) were diagnosed with abdominal obesity.ConclusionOur research has revealed compelling new evidence about the obesity epidemic among Chinese adults aged >= 40 years, particularly at the provincial and ethnic levels. As a result, more targeted and effective prevention strategies should be developed to alleviate the burden of obesity.