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.