Objective: This study aimed to verify the application values of the Chinese Group on the Study of Severe Hepatitis B (COSSH) acute-on-chronic liver failure(ACLF)Ⅱ score in predicting short-term prognosis and stratifying disease severity in patients with hepatitis B virus - related ACLF(HBV -ACLF). Methods: Clinical data and survival information of 114 patients admitted with HBV-ACLF to the First Affiliated Hospital of Wannan Medical College from January 2017 to December 2021were retrospectively evaluated. Baseline characteristics were compared between the survival group(n=67)and the death group (n=47)at day 90 from inclusion. Prognostic accuracies between the COSSH ACLFⅡ score and the COSSH ACLF score, the Chronic Liver Failure-Consortium(CLIF-C) ACLF score, the CLIF -C organ failure(CLIF -C OF)score, the model of end - stage liver disease(MELD)score, the MELD - sodium (MELD-Na)score, and the Child-Turcotte-Pugh(CTP)score in 90-day mortality prediction were compared using the area under the receiver operating characteristic curve(AUC)method. All patients were divided into three groups according to COSSH ACLF grade (ACLF-1, n=83;ACLF-2, n=23;ACLF-3, n=8)or the risk strata of the COSSH ACLFⅡ score (<7.4, n=82;7.4~<8.4, n=21; and ≥8.4, n=11), and the cumulative 90- day survival rates among them were compared using the Kaplan -Meier method. Results: Compared with the survival group, the death group had greater age, a higher incidence of hepatic encephalopathy or bacterial infection, higher values of white blood cell count, neutrophil count, international normalized ratio, total bilirubin, creatinine, urea, and the above-mentioned 7 scores(P < 0.05). The incidence of coagulation failure or cerebral failure and the proportion of patients with ACLF-1 in the death group were also higher than those in the survival group(P < 0.01). For 90-day mortality prediction, the AUC of COSSH ACLFⅡ score(0.892)was larger than that of the CLIF-C ACLF score(AUC=0.853, P=0.089), the COSSH ACLF score(AUC=0.841, P < 0.05), the CLIF-C OF score(AUC=0.813, P<0.05), the MELD-Na score(AUC=0.771, P < 0.01), the MELD score(AUC=0.792, P < 0.01), and the CTP score(AUC=0.655, P < 0.001). The cumulative 90- day survival rates significantly decreased with COSSH ACLF grade and risk strata of the COSSH ACLFⅡ score ascending(73.5% vs. 26.1% vs. 0, P < 0.001;72.0% vs. 38.1% vs. 0, P<0.01). Conclusion: The COSSH ACLFⅡ score showed excellent prognostic performance in predicting short-term prognosis in patients with HBV-ACLF. Using risk strata of the new score can simplify the severity stratification of HBV-ACLF. [ABSTRACT FROM AUTHOR]