CA19-9 is a glycoprotein, which is a commonly used tumor marker in clinical practice. It is usually used for the following purposes: First, it is one of the laboratory indicators needed for early cancer screening for general or high-risk groups. Secondly, after patients are diagnosed with tumor, the effect of treatment can be judged according to the level of CA19-9. CA19-9 can be used as an indicator for long-term follow-up after the treatment of tumor patients. If CA19-9 continues to increase, it often indicates the possibility of tumor recurrence and metastasis. In conclusion, CA19-9 is a commonly used tumor marker. It is necessary to know that CA19-9 is also increased in many benign diseases, while malignant tumors do not necessarily show increased CA19-9, so it is necessary to judge and analyze the causes of abnormal CA19-9 in a comprehensive and reasonable way in clinical practice.