Inclusion Criteria:  Able to provide written informed consent and can understand and agree to comply with the requirements of the study and the Schedule of Assessments Age ≥ 18 years on the day of signing the informed consent form (or the legal age of consent in the jurisdiction in which the study is taking place) Disease progression from prior chemotherapy and anti-PD-(L)1 therapy (including sequential or combined therapy, regardless of the order) No antiPD-1/PD-L1 related toxicity during the prior treatment Have not received other immunotherapy, including but not limited to anti-OX40, anti-TIGIT and anti-CD137, etc. BRAF wild-type patients, or patients with BRAF mutations who are not suitable or refused to receive targeted therapy with BRAF inhibitors and/or MEK inhibitors Have not been exposed to small molecule targeted drugs with anti-angiogenesis effect, or VEGFR TKI drugs Eastern Cooperative Oncology Group (ECOG) Performance Status ≤ 1 Adequate hematologic and end-organ function Have not received radiotherapy, endocrine therapy, molecular targeted therapy, or surgery within 2 weeks before the start of the study, and have recovered from the acute toxicity of the previous treatment Females of childbearing potential must be willing to use a highly effective method of birth control for the duration of the study, and ≥ 120 days after the last dose of study drugs and have a negative serum pregnancy test ≤ 7 days of first dose of study drugs  Exclusion Criteria:  Ocular melanoma known NRAS mutations Active leptomeningeal disease or brain metastases that are not well controlled. History of active autoimmune disease Any active malignancy ≤ 2 years Any condition that required systemic treatment with either corticosteroids (> 10 mg daily of prednisone or equivalent) or other immunosuppressive medication ≤ 14 days before first dose of study drugs History of interstitial lung disease, noninfectious pneumonitis or uncontrolled diseases, including pulmonary fibrosis, acute lung diseases, etc. Severe chronic or active infections (including tuberculosis infection, etc.) requiring systemic antibacterial, antifungal or antiviral therapy, within 14 days prior to first dose of study drugs Known history of HIV infection Any major surgical procedure requiring general anesthesia ≤ 28 days before first dose of study drugs Prior allogeneic stem cell transplantation or organ transplantation Hypersensitivity to tislelizumab or sitravatinib, to any ingredient in the formulation, or to any component of the container Bleeding or thrombotic disorders or use of anticoagulants such as warfarin or similar agents requiring therapeutic INR monitoring within 6 months before first dose of study drugs Concurrent participation in another therapeutic clinical trial