Acute-on-chronic liver failure （ACLF） is a syndrome with high mortality triggered by acute predisposing factors in patients with underlying chronic liver diseases. Clinical studies have shown that ACLF can be reversed to a certain degree， and early intervention can improve patient prognosis， whereas delayed diagnosis and treatment can lead to a significant increase in mortality. In recent years， scholars in this field have proposed the concept of “pre-acute-on-chronic liver failure （Pre-ACLF）”， which aims to improve clinical outcomes through early identification and intervention. This article systematically reviews the origin of the Pre-ACLF concept and its latest definitions in China and globally， summarizes the latest research advances in Pre-ACLF in terms of traditional clinical-laboratory parameters， high-throughput omics， and molecular biological mechanisms， and proposes the important clinical need for further unifying the definition of Pre-ACLF.