Inclusion Criteria:

          1. Age ≥ 18 years but ≤ 75 years

          2. Being able to follow the protocol requirements as per investigator's evaluation.

          3. Provide written informed consent before any protocol-related procedure (that is not a
             part of subject's routine care) is carried out.

          4. Unresectable locally advanced or metastatic gastric carcinoma (GC) or
             gastro-esophageal junction (GEJ) carcinoma, and have histologically confirmed
             predominant adenocarcinoma.

          5. The subject may have at least a measurable lesion or an evaluable lesion, if not
             measurable; the investigator will carry out evaluation according to Response
             Evaluation Criteria in Solid Tumors (RECIST) v1.1 within 28 days prior to
             randomization.

          6. Eastern Cooperative Oncology Group performance status (ECOG PS) 0 or 1.

          7. Expected survival ≥ 3 months.

          8. Subject must not have received systemic treatment (including HER2 inhibitor) for
             advanced or metastatic gastric carcinoma.

          9. Subject must provide tumor tissue samples for biomarker analysis in order to determine
             the expression of PD-L1.

         10. Permitted prior treatment: Subjects with GC or GEJ carcinoma priorly treated with
             adjuvant or neoadjuvant therapy, who experience clinical progression of disease at
             least 6 months during treatment or after treatment are allowed to be enrolled.

         11. Subjects must have adequate organ function as assessed in the laboratory tests

         12. Subjects with active hepatitis B or active hepatitis C must receive antiviral
             treatment for at least 14 days prior to the first dose of study treatment and pass the
             hepatitis B virus (HBV) DNA titer test (≤ 500 IU/mL or 2500 copies/mL) and hepatitis C
             virus (HCV) RNA test (≤ lower limit of detection) before being enrolled. The subject
             should be willing to continue effective anti-viral treatment during the study.

         13. Female subject with childbearing potential must have negative serum pregnancy test
             result at screening, except for those with available sterilization operation record or
             post-menopausal subjects. Female subject with childbearing potential or male subjects
             and their partners must agree to take effective contraceptive measures from the day of
             signing ICF till at least 6 months after the last dosing of investigational product.

        Exclusion Criteria:

          1. Known HER-2 positivity.

          2. A known additional primary malignancy that occurred within 5 years prior to the first
             dose of investigational treatment, except for locally curable cancers that have been
             apparently cured, such as basal or squamous cell skin cancer, superficial bladder
             cancer, or carcinoma in situ of the prostate, cervix, or breast.

          3. Known primary central nerve system (CNS) tumor or meningeal metastasis, or unstable
             CNS metastasis (symptomatic within 4 weeks before first dose of investigational
             product, requiring corticosteroid treatment, or without radiologic evidence supporting
             stable status for over 4 weeks prior to the first dose of investigational product).

          4. Any severe or uncontrolled systemic disease, for example diabetes mellitus or
             hypertension, that may increase the risk associated with participation or
             investigational product administration, or compromise subject's ability to receive
             investigational product, as per investigator's judgment.

          5. Known positive human immunodeficiency virus (HIV) or acquired immunodeficiency
             syndrome (AIDS).

          6. Has had prior chemotherapy, immune therapy, biological therapy (including cancer
             vaccine, cytokine therapy or growth factors to control cancer) used as systemic
             treatment for cancer, within 14 days before the first dose of investigational product.

          7. Any prior treatment of antibody/drug that targets at T-cell coregulatory proteins or
             immune checkpoints pathways(including anti-PD-1, anti-PD-L1, anti-CTLA4, anti-TIM3,
             anti-LAG3 antibody, etc.).

          8. Subjects with conditions that in the investigator's opinion are not suitable for
             participating in this trial.