Inclusion Criteria:
* Subjects participate voluntarily and sign informed consent.
* 18-75 years, male or female.
* Histologically confirmed Unresectable Advanced or metastatic Esophageal Squamous Cell Carcinomas
* No previous systemic anti-tumor treatment for unresectable locally advanced or metastatic esophageal squamous cell carcinoma has been received
* At least 1 measurable target lesion and/or unmeasurable target lesion according to Response Evaluation in Solid Tumors (RECIST 1.1).
* ECOG PS 0-1
* Expected survival ≥ 12 weeks
* Adequate organ function (without blood transfusion or growth factors within 14 days prior to first dose), including: ANC ≥ 1.5 × 10⁹/L; Platelets ≥ 100 × 10⁹/L; Hemoglobin ≥ 90 g/L; Serum albumin ≥ 30 g/L; Total bilirubin ≤ 1.5 × ULN; ALT/AST ≤ 2.5 × ULN (≤ 5 × ULN if with liver or bone metastases); ALP ≤ 2.5 × ULN; Serum creatinine ≤ 1.5 × ULN; INR ≤ 1.5 (if not on anticoagulation);
* Non-sterilized women of childbearing potential and male participants with such partners must agree to use medically approved contraception during and for 3 months after study drug administration. Women must test negative for serum or urine HCG within 7 days prior to first dose and not be breastfeeding
Exclusion Criteria:
* Have received anti-PD-1 or anti-PD-L1 antibody therapy;
* BMI \< 18.5 kg/m2 or weight loss ≥ 10% within 2 months before screening (at the same time, the effect of a large amount of pleural effusions and ascites on bogy weight should be considered);
* Presence of any active autoimmune disease or history of autoimmune disease (such as: Autoimmune hepatitis, interstitial pneumonia, uveitis, enteritis, hypophysitis, nephritis, hyperthyroidism)
* Those who are taking immunosuppressants or systemic hormonal therapy for immunosuppressive purposes (dose\> 10 mg/day prednisone or other equivalent cortiremonial hormones)
* Severe allergic reaction to other monoclonal antibodies
* Known history or evidence of interstitial lung disease or active non-infectious pneumonia
* Known central nervous system metastases
* History of other malignancies within the past 5 years or concurrent malignancies (except for cured basal cell carcinoma of the skin and carcinoma in situ of the cervix).
* Uncontrolled cardiac clinical symptoms or diseases, such as: (1) NYHA class II or higher heart failure (2) unstable angina (3) myocardial infarction within the past year (4) clinically significant supraventricular or ventricular arrhythmias requiring treatment or intervention (5) QTc \> 450 ms (male); QTc \> 470 ms (female)
* Tumor invasion of major blood vessels, or based on imaging, the investigator determines a high likelihood of tumor invasion of major blood vessels during the study period, which may lead to fatal bleeding, such as imaging evidence of \>90-degree encasement of major vessels or tumor cavitation
* Patients with pleural effusion, ascites, or pericardial effusion requiring drainage; if the symptoms are stable after drainage as assessed by the investigator, enrollment is possible. Gastrointestinal fistula, gastrointestinal perforation, or intra-abdominal abscess within 6 months prior to the start of study treatment.
* Major surgical procedures within 4 weeks prior to the start of study treatment (diagnostic procedures excluded) or anticipated need for major surgery during the study period.
* Active infection, unexplained fever ≥38.5°C within 7 days prior to drug administration, or baseline white blood cell count \>15×109/L.
* Congenital or acquired immunodeficiency (e.g., HIV infection); hepatitis B surface antigen (HBsAg) positive with hepatitis B virus deoxyribonucleic acid (HBV DNA) ≥2000 IU/ml, or positive for hepatitis C virus antibody.
* Live vaccine administration within 4 weeks prior to study drug administration or during the study period.
* As judged by the investigator, other factors that may affect study outcomes or lead to premature termination of the study, such as alcoholism, drug abuse, other serious diseases (including psychiatric disorders) requiring concurrent treatment, significant laboratory abnormalities, or family or social factors that may impact patient safety.
