We aimed to assess the epidemiological characteristics of hepatitis B virus (HBV) infection in Chinese adults at different phases of the coronavirus disease 2019 (COVID‐19) pandemic, that is, before, during the pandemic, and after the easing of restrictive measures. We included 20,357 adult patients who visited Mianyang Hospital and had hepatitis B DNA tests from January 1, 2018, to June 30, 2023. Clinical information and HBV test results were extracted from the laboratory information system. We calculated the positive rate of HBV detection by age groups, gender, seasons, types of patients, and stages of the COVID‐19 pandemic. Nonlinear associations between age and risk of HBV infection in three stages of the pandemic were assessed by restricted cubic spline regression models. Among 20,357 patients, 2,670 (13.1%) were tested as positive. The highest positive rate was observed in the 18-25 age group (i.e., 16%). HBV infection showed an insignificant pattern among seasons. Although there is no statistical significance regarding the positive rate at three phases of the pandemic, we observed that the rate went high during the pandemic and saw a sharp decline after easing the measures among the population ( p < 0.05), which consisted of our regression models. In addition, regression analyses suggested that the age effect became weaker after easing all restrictive measures compared with other stages. Based on our findings, we called for attention from health professionals and caregivers on the new epidemiological characteristics of HBV infection in advance to deal with the potential increase under restrictive measures.