Acute-on-chronic liver failure is a characteristic clinical liver syndrome, which should be differentiated from acute liver failure, acute decompensated liver cirrhosis and chronic liver failure. The pathogenesis of ACLF is not fully understood yet. Viral factors and immune injury have been reported to be the two major pathogenesis. This paper reviewed the researches on the pathogenesis of acute on chronic hepatitis B liver failure in recent years, to provide theoretical basis for prompt and accurate diagnosis and treatment of this syndrome. This would beneift for the prognosis and raise the survival rate of patients.