Gastric cancer is one of the most common malignant tumors throughout the body and the number one cause of death due to malignant tumors. In China, gastric cancer occupies the first place of gastrointestinal malignancies and the third place of systemic malignancies [1]. In the past 10 years or so, various methods have been used to improve the treatment effect of gastric cancer and some progress has been made, but in general, the treatment effect of gastric cancer is still unsatisfactory. Since the stomach is located deep in the abdominal cavity, there are no specific signs and symptoms in the early stage, and patients are often in the middle and late stages when they are seen, only about 85% of them are operable, and half of them are resectable. Among the resected lesions, only half of them are curable again [2]. Therefore, early diagnosis is the key to the treatment of gastric cancer, and a more specific tumor marker would be of considerable clinical help. In view of this, many researches have been conducted in this area, and the progress has been faster in recent years, which are reviewed as follows. Tumor markers are mainly substances secreted or shed into body fluids or tissues by tumor cells, or substances produced and secreted into body fluids or tissues by hosts in response to new biological reactions in vivo. These substances do not exist in normal adult tissues but are found in embryonic tissues, or when tumors increase in size, their content greatly exceeds the amount in normal conditions, so they can be used to indicate the existence of tumors, to identify the nature of tumors, to understand the tissue differentiation, cellular differentiation and cellular functions of tumors, to help classify tumors, or to help judge prognosis and guide treatment, and therefore are increasingly important and developing rapidly. Nowadays, there are more than 200 tumor markers reported from biochemistry and immunology, and 20-30 of them are commonly used in clinical practice, but there are not many tumor markers for gastric cancer, and they lack indicators with high sensitivity and specificity. CEA is elevated in patients with various tumors, especially in gastrointestinal tumors, which have higher sensitivity. According to the report, the positive rate of CEA in serum of all stages of gastric cancer is 8%-62.5%, and the positive rate has a great relationship with the prognosis of tumor stage, and its correlation with the depth of tumor infiltration is obvious and can suggest distant metastasis. kim et al. detected CEA in serum of gastric cancer patients by radioimmunoassay and found that preoperative CEA>10.0mg/L is more CEA.