Early identification of hepatitis B virus-related acute-on-chronic liver failure (HBV-ACLF) holds crucial importance in guiding clinical management and reducing mortality. However, existing scoring systems often overlook patient's underlying clinical condition, which significantly impacts prognosis. Use the age-adjusted Charlson comorbidity index (aCCI) to evaluate the patient's complications to develop a more precise model for predicting transplant-free mortality in HBV-ACLF patients. Nine hundred and six patients were included for investigation and were segregated into a training cohort and a temporal validation cohort according to the chronological order of admission in a ratio of 7:3. In the training cohort, univariate analysis, logistic regression analysis and LASSO regression analysis were used to construct a prognostic model and it was subsequently validated in a temporal validation cohort and an external validation cohort. We found total bilirubin, neutrophils, international normalised ratio and aCCI exhibited significant associations with 28-day transplant-free mortality and established a novel prognostic model, named aCCI-HBV-ACLF. The model demonstrated strong predictive performance, with area under the receiver operating characteristic curve (ROC) values of 0.859 for 28-day mortality, 0.822 for 90-day mortality. In the temporal validation cohort, aCCI-HBV-ACLF achieved area under the ROC values of 0.869 for 28-day mortality and 0.850 for 90-day mortality. In the external validation cohort, aCCI-HBV-ACLF had area under the ROC values of 0.868 for 28-day mortality and 0.888 for 90-day mortality. This study proposes a new prognostic model, which achieved excellent predictive ability for 28-/90-day transplant-free mortality rates among patients with HBV-ACLF.