Under the effect of external environmental factors, especially chemical agents, radioactive substances and other carcinogenic factors, mutated tumor cells often appear in healthy human body, but most human body does not develop the disease. This is because the immune system of human body protects the human body like a guard, which carries out “immune defense” against bacteria and other pathogenic microorganisms, and “immune surveillance” against its own mutated tumor cells, and constantly removes the tumor cells that appear at any time. However, as people grow older, especially in old age, their physiological functions begin to show progressive decline and the function of immune system gradually decreases, so once a few mutated tumor cells escape from “immune surveillance”, they may gradually grow into tumors. Therefore, people should start to pay attention to cancer prevention checkups in their old age. So what are the easy and simple serological cancer prevention tests and how to choose them? Tumor markers are some special substances produced in human body, and their content in tumor patients is significantly higher than normal people, so measuring their content through serum or plasma can provide a basis for early diagnosis of cancer, so it is imaginatively called the vane of tumor diagnosis and treatment. CEA, Cyfra211, NSE, SCC can be chosen for long-term unexplained cough and blood coughing suspected of lung tumor; CEA, CA199, CA724, CA242 can be chosen for stomach pain, blood vomiting, blood in stool suspected of gastrointestinal tumor; CEA, AFP, CA199 can be chosen for liver and biliary tumor; CEA, CA199, CA242 can be chosen for pancreatic tumor; CEA, CA153 can be chosen for breast tumor. CEA, CA153 for breast tumors; SCC for cervical tumors; CA125 for ovarian tumors; PSA for prostate tumors. These tests are now widely used in clinical practice.