• Age ≥18 years old, male or female;

• Advanced, metastatic or recurrent malignant tumors diagnosed by histology or pathology, mainly colorectal cancer, esophageal cancer, gastric cancer, and pancreatic cancer;

• After receiving at least second-line standard treatment and failing (disease progression or intolerance, such as surgery, chemotherapy, radiotherapy, etc.) or lack of effective treatment methods;

• Immunohistochemical staining of tumor samples within 3 months confirmed that the tumor was CEA positive (clear membrane staining, positive rate ≥ 10%); the patient's serum CEA should exceed 10ug/L.

• At least one assessable lesion according to RECIST 1.1 criteria;

• ECOG score 0-2 points;

• No serious mental disorder;

• Unless otherwise specified, the function of the vital organs of the subject shall meet the following conditions:

∙ Blood routine: white blood cells\>2.0×109/L, neutrophils\>0.8×109/L, lymphocytes cells\>0.5×109/L, platelets\>50×109/L, hemoglobin\>90g/L;

‣ Cardiac function: echocardiography showed cardiac ejection fraction ≥50%, and no obvious abnormality was found on electrocardiogram;

‣ Renal function: serum creatinine≤2.0×ULN;

‣ Liver function: ALT and AST ≤3.0×ULN (for those with liver tumor infiltration, it can be relaxed to≤5.0×ULN);

‣ Total bilirubin≤2.0×ULN;

‣ Oxygen saturation \> 92% in non-oxygen state.

• Have apheresis or venous blood collection standards, and have no other contraindications for cell collection;

⁃ Subjects agree to use reliable and effective contraceptive methods for contraception within 1 year after signing the informed consent form to receiving CAR-T cell infusion (excluding rhythm contraception);

⁃ The patients themselves or their guardians agree to participate in this clinical trial and sign the ICF, indicating that they understand the purpose and procedures of this clinical trial and are willing to participate in the research.