Alpha fetoprotein （AFP） is a single chain glycoprotein synthesized by fetal liver cells and is a special protein normally present in fetal serum. About two weeks after the birth of the fetus, alpha fetoprotein disappears from the blood, and the content of alpha fetoprotein in the serum of normal people is less than 20 ng/ml. In adults, alpha fetoprotein increases can be seen in primary liver cancer, active liver disease, reproductive system tumors, pregnant women, pancreatic cancer and lung cancer. Alpha fetoprotein is currently the most widely used serum marker for auxiliary diagnosis of liver cancer in clinical practice. Serum alpha fetoprotein and liver ultrasound are the main means of early screening for liver cancer.