Chemoradiotherapy（CRT） is the main treatment for esophageal cancer patients with recurrent desease，and checkpoint blockade (PD-1) have been shown to be effective in advanced esophageal cancer. Therefore, PD-1 combined with chemoradiotherapy （CRT）may further improve the efficacy and become a new method for the treatment of esophageal cancer.This study intends to conduct a single-arm, prospective clinical study, aiming to evaluate the safety and efficacy of PD-1 combined with chemoradiotherapy(CRT) in patients with oligometastatic esophageal squamous cell carcinoma.

Inclusion Criteria:

•≥18 years；

• Esophageal squamous cell carcinomas；
• After radical treatment including surgery or definitive chemoradiotherapy
• Definition of oligometastases：≤3 metastases, including tumor beds and recurrent anastomotic sites；regional lymph node is defined as one metastatic site（AJCC8th, supraclavicular, mediastinal, abdominal）；metastases lesion in liver, lung, bone and brain is no more than 1.
• Karnofsky performance status(KPS)≥ 70；
• No immunotherapy were performed after recurrence；
• a white-cell count of at least 3500G/L, a hemoglobin concentration of at least 100 g/L, a platelet count of at least 100,000/lL, aspartate aminotransferase and alanine aminotransferase levels of within 1.5 times the upper limit of normal, a serum bilirubin level of 1.5 mg/dL or less, a creatinine level of 1.1 mg/dL or less;
• Hepatitis virus indicators: normal or hepatitis virus DNA titer less than 500 at the same time in an infectious disease hospital, and with the consent of the doctor can be treated；

Exclusion Criteria:

• Pregnancy, possible pregnancy, or breast-feeding;
• Psychological, family, social and other factors lead to uninformed consent;
• An esophageal mediastinal fistula and/or an esophageal tracheal fistula prior to treatment;
• Serious complications such as ischemic heart disease, arrhythmias, or other types of heart disease requiring treatment; liver cirrhosis; interstitial pneumonia or pulmonary fibrosis; active gastrointestinal bleeding; mental disorders being treated with antipsychoticagents or requiring treatment;
• Controlled diabetes mellitus;
• A history of autoimmune disease, autoimmune disease (such as colitis, hepatitis, hyperthyroidism, including but not limited to these disease or syndrome) and a history of immune deficiency, including test positive for HIV, or has other acquired, congenital immunodeficiency disease, or have a history of organ transplantation and the history of allogeneic bone marrow transplantation;
• A history of interstitial lung disease and a history of non-infectious pneumonia;
• Active hepatitis B (HBV DNA ≥ 2000 IU/mL or 104 Copies /mL), hepatitis C ;(positive HCV antibody and HCV-RNA above the detection threshold of the assay）
• Any situation that is unstable or may compromise patient safety and compliance ;
• Active infections, such as active tuberculosis, are present;