Inclusion Criteria:  Age ≥18 years old and ≤75 years old, regardless of gender; Histologically or cytologically confirmed recurrent or metastatic esophageal squamous cell carcinoma; Non-regional lymph node metastasis, such as upper neck, retroperitoneal or axillary lymph node metastasis; or distant metastasis, but no more than 3 metastatic organs, and no more than 5 lesions; Patients who have not received other systems of anti-tumor treatment; the patients who have received neoadjuvant/adjuvant and radical concurrent radiochemotherapy, and the last treatment time or progress time exceeds 6 months; Patients who have not progressed after receiving 4 courses of chemotherapy combined with PD-1 immune checkpoint inhibitor treatment (according to the RECIST 1.1 evaluation standard); There are measurable lesions according to the RECIST 1.1 standard (cavity structures such as the esophagus cannot be used as measurable lesions), and the measurable lesions should not have received local treatment such as radiotherapy; ECOG PS score is 0～1; For non-surgically sterilized female patients of childbearing age, the serum or urine HCG test must be negative within 72 hours before randomization; Volunteer to participate in clinical research: fully understand and know the research and sign the Informed Consent Form (ICF); willing to follow and have the ability to complete all trial procedures; Have not received immunotherapy or biological therapy before; Hemoglobin ≥90g/L, platelets ≥10×10 9 /L, absolute neutrophil count ≥1.5×10 9 /L; Serum creatinine ≤ 1.5 times UNL; Serum bilirubin≤1.5×UNL, AST (SGOT) and ALT (SGPT)≤2.5×UNL, alkaline phosphatase≤5×UNL; Coagulation function: INR≤1.5 × ULN; if the patient is receiving anticoagulation therapy, PT or APTT is within the acceptable range of treatment; There was no history of interstitial pneumonia or previous interstitial pneumonia.  Exclusion Criteria:  In addition to the systemic treatment recommended by this program, patients have received other immune checkpoint inhibitor treatments such as anti-PD-1, anti-PD-L1, anti-PD-L2, anti-CD137, or anti-CTLA-4 antibodies in the past, or any other antibodies or drugs with specific targets for T cell costimulation or checkpoint pathways; Patients have received radiotherapy in the past, and the tumor in the irradiation field has progressed; BMI<18.5kg/m 2 , or weight loss >10% within 2 months before screening ; With brain metastases; With metastasis of the meninges, pleura or pericardium; Esophageal perforation and active esophageal bleeding, with invasion of trachea and large blood vessels in the thoracic cavity; Those who confirmed tumor progression during systemic treatment (RECIST 1.1 standard); Severe symptoms of dysphagia caused by tumor compression require immediate radiotherapy intervention to relieve the obstruction; Systemic treatment toxicity did not return to ≤ CTCAE level 1 (except for hair loss) or the level specified by the inclusion/exclusion criteria; Subjects have cardiovascular diseases or clinical symptoms that are not well controlled, including but not limited to: (1) Heart failure above NYHA II; (2) Unstable angina; (3) Myocardial infarction within 1 year; ( 4) Clinically significant supraventricular tachycardia or ventricular arrhythmia without clinical intervention, or poor control after clinical intervention; Patients with severe lung disease, interstitial pneumonia, or previous history of interstitial pneumonia: Autoimmune diseases (such as: systemic lupus erythematosus, rheumatoid arthritis, inflammatory bowel disease, autoimmune thyroid disease), but allow the following diseases to enter the next step of screening: type I diabetes, skin diseases that do not require systemic treatment ( Such as vitiligo, psoriasis); Patients have active hepatitis B (HBV DNA≥2000IU/L or 104copies/ml) or hepatitis C (hepatitis C antibody is positive, and HCV-RNA is higher than the detection limit of the analysis method); Suffered from an active infection requiring systemic treatment 14 days before the first administration; Patients with active pulmonary tuberculosis infection found through medical history or CT examination, or patients with a history of active pulmonary tuberculosis infection 1 year before enrollment, or patients with active pulmonary tuberculosis infection more than 1 year ago but without formal treatment; Patients with other malignant lesions, except for curable skin cancer (non-melanoma), cervical carcinoma in situ or malignant disease cured ≥ 5 years; Patients who cannot understand the test requirements or may not comply with the test requirements; The investigator believes that some obvious diseases should be excluded from this study; The dose limit of radiotherapy cannot meet the limit requirement set by this study.