Key Inclusion Criteria:

          -  Histopathologically confirmed unresectable, locally advanced, recurrent or metastatic
             ESCC (excluding mixed adenosquamous carcinoma and other histological subtypes)

          -  ECOG PS of 0 or 1

          -  Subject must be unsuitable for definitive treatment, such as definitive
             chemoradiotherapy and/or surgery. For subjects who have received (neo)adjuvant or
             definitive chemotherapy/radiochemotherapy, time from the completion of last treatment
             to disease recurrence must be > 6 months Could provide archival or fresh tissues for
             PD-L1 expression analysis with obtainable results#

          -  Have at least one measurable lesion as per RECIST v1.1

        Key exclusion Criteria:

          -  ESCC with endoscopy-confirmed near-complete obstruction requiring interventional
             therapy

          -  Post stent implantation in the esophagus or trachea with risk of perforation

          -  Received systemic treatment for advanced or metastatic ESCC.

          -  Received a Cumulative dose of cisplatin > 300 mg/m2 within 12 months to randomization.

          -  High risk of hemorrhage or perforations due to tumor invasion in adjacent organs
             (aorta or trachea), or have fistula formation.

          -  Hepatic metastasis > 50% of the total liver volume.

          -  Received palliative therapy for a local lesion within 2 weeks prior to the first dose.

          -  Received systemic treatment with Chinese traditional medicines with anti-cancer
             indications or immunomodulators (including thymosins, interferons, and interleukins)
             within 2 weeks prior to the first dose of study treatment.

          -  Received systemic immunosuppressants within 2 weeks prior to randomization, excluding
             local use of glucocorticoids administered by nasal, inhaled, or other routes, and
             systemic glucocorticoids at physiological doses (no more than 10 mg/day of prednisone
             or equivalents), or glucocorticoids to prevent allergies to contrast media.