Objective: To analyze the prevalence and related factors of HBV infection among people aged 18 years old and above in Mianyang city. Methods: A total of 260 950 residents, living in Mianyang city more than 6 months, aging 18 years old and above were employed by multi-stage random sampling method from November 2014 to September 2015. Questionnaire survey was conducted on participants using a self-designed questionnaire, including general demographic characteristics, family history of Hepatitis B, history of Hepatitis B vaccination and history of present illness, etc. 5ml blood was collected from all participants, and the blood samples were detected for HBsAg by enzyme-linked immunosorbent assay (ELISA). The multivariate unconditional logistic regression was performed to identify the related factors of positive HBsAg. Results: Among the 260 950 subjects, 113 184 were males (43.37%), 147 766 were females (56.63%), and the average age was (47.68±17.36) years old. The positive rate of HBsAg was 6.10%(15 822 cases). Subjects who were 25-34 years old (OR=1.23), 35-44 years old (OR=1.26), 45-54 years old (OR=1.23), and 55-64 years old (OR=1.34) were more likely to be HBsAg positive,65 years and older (OR=0.88) were less likely to be, compared with subjects aging 18-24 years old; males were more likely to be HBsAg positive compared with females (OR=1.35); people living in Fucheng district were more likely to be HBsAg positive compared with who living in Jiangyou district(OR=1.91); married people were more likely to be HBsAg positive compared with unmarried ones (OR=1.36); medical staff were less likely to be HBsAg positive compared with non-medical staff (OR=0.61); subjects with a surgery history were more likely to HBsAg positive compared with who without (OR=1.13); subjects with trauma history were more likely to HBsAg positive compared with who without (OR=1.13); people with history of Hepatitis B were more likely to HBsAg positive compared with who without (OR=4.21); people with Hepatitis B vaccination history were less likely to be HBsAg positive compared with who without (OR=0.48); all the P values above were less than 0.05. Conclusion The positive rate of HBsAg among adults in Mianyang city was very high, and we should pay more attention to people aging between 25 and 64 years old, male, medical staff, with surgery history, trauma history, and a family history of Hepatitis B and Hepatitis B vaccination history.