Carcinoembryonic antigen (CEA) is an acidic protein. Normal mucosa adjacent to cancer contains little or negative CEA. The CEA positivity rate of gastric cancer is 85.58%. Among them, 100% were mucinous adenocarcinoma and impression cell carcinoma (mucinous cell carcinoma). Under the electron microscope, CEA was distributed in the membrane of cancer cells and the organelles of protein synthesis and transportation (such as nuclear membrane, endoplasmic reticulum, Golgi apparatus and its secretory vesicles) in the cytoplasm of cancer cells, suggesting that the synthesis of CEA by cancer cells was increased, and the CEA entering the glandular lumen was increased. Since CEA was located in the sugar envelope around the cell membrane and was easily released into the surrounding body fluids, the concentration of CEA in body fluids and gastric fluids was higher than that in the blood serum. The reason for the higher content of CEA in the cytoplasm of cancer cells is related to the increased synthesis of CEA in cancer cells and the obstruction of CEA efflux. When cancer cells are degenerated and necrotic, the intracellular membrane structure is damaged and ruptured, and CEA can appear in the matrix of cytoplasm. Immunoelectron microscopy showed that mucinous cell carcinoma CEA was distributed in the membrane structure of the whole cell membrane and cytoplasm, and the determining base of CEA antigen was glycoprotein, and the infiltration and metastasis of tumor cells were related to the alteration of glycosylation of cell membrane glycoproteins. In addition, mucinous cell carcinoma can also secrete and release a large amount of protein hydrolases, which can destroy the calcium bridge of cancer cells and dissolve the soft tissues around cancer nests. Therefore, gastric mucinous cell carcinoma has strong invasive force and high metastatic rate.