This study is a single-arm, prospective, open-label clinical study to evaluate the safety and efficacy of tislelizumab combined with chemoradiotherapy in first-line treatment of patients with stage IVb esophageal squamous cell carcinoma.

This study is a single-center, prospective, single-arm, open-label study. It will explore the efficacy and safety of tislelizumab combined with nab-paclitaxel in the first-line treatment of stage IVb esophageal squamous cell carcinoma on the basis of low-dose radiotherapy（40Gy/20f，5次/w）. To explore new treatment modalities and prolong patient survival.

Inclusion Criteria:

1. Meet the diagnostic criteria of Esophageal squamous cell carcinoma

   -diagnosed with stage IVb Esophageal squamous cell carcinoma (UICC/AJCC 8th edition TNM staging system) by CT/MRI/PET-CT/ECT, laboratory examination and pathological examination results; specific: any T, any N, M1;

2. No previous anti-tumor treatment; expected survival period of more than half a year; 3.18-75 years old, PS score 0-1;

4. According to RECIST1.1 criteria, there is at least one measurable target lesion, and tumor imaging evaluation is performed within 28 days before the first dose; 5. Major organ function is normal, that is, the following criteria are met: 6. No active autoimmune disease; 7. No active hepatitis; 8. General conditions or medical complications can tolerate radiotherapy, chemotherapy and immunotherapy; 9. No history of malignant tumor, no previous anti-tumor therapy; 10. For premenopausal or surgically sterilized female patients: Consent to abstinence or use of effective contraception during treatment and for at least 7 months after the last dose of study treatment; 11. Understand and sign the informed consent form for this study.

Exclusion Criteria:

1. Previous antitumor therapy or radiation therapy for any malignant tumor;
2. patients receiving standard treatment;
3. concurrently receiving anti-tumor therapy in other clinical trials, including endocrine therapy, bisphosphonate therapy, or immunotherapy;
4. Has undergone major surgical procedures unrelated to colorectal cancer within 4 weeks prior to enrollment, or the patient has not fully recovered from such surgical procedures;
5. Serious heart disease or discomfort, including but not limited to the following:
6. Inability to swallow, bowel obstruction, or other factors that interfere with drug taking and absorption;
7. Known history of allergy to the drug components of this regimen; history of immunodeficiency, including positive HIV test, positive HBV/HCV test, or other acquired or congenital immunodeficiency diseases, or a history of organ transplantation;
8. Pregnant or lactating female patients, female patients of childbearing potential with a positive baseline pregnancy test, or patients of childbearing age who are unwilling to take effective contraceptive measures throughout the trial period and within 7 months after the last study drug;
9. Have serious comorbidities or other comorbidities that would interfere with planned treatment, or any other condition that the investigator considers the patient unsuitable for participation in this study.

This study is a single-arm, prospective, open-label clinical study