Inclusion Criteria:  Male or female ≥ 18 years of age Eastern Cooperative Oncology Group (ECOG) Performance Status of 0-2 Participants must have histologically or cytologically confirmed diagnosis of adenocarcinoma of the colon or rectum, with clinical confirmation of unresectable and/or metastatic disease that is measurable according to Response Evaluation Criteria in Solid Tumors (RECIST 1.1) criteria Presence of BRAF V600E in tumor tissue determined by local assay at any time prior to screening and confirmed by central laboratory. And confirmation of MSS or pMMR status from immunohistochemistry or PCR or NGS; Prior treatment with at least one systemic treatment (chemotherapy or target therapy) for mCRC, and prior treatment did not include cetuximab  Adequate organ and marrow function:  ①Hemoglobin (Hb) ≥ 90 g/L；Platelets (PLT) ≥ 75 x 10^9/L；Neutrophil ≥1.5 x 10^9/L ②Total bilirubin ≤ 1.5 x upper limit of normal (ULN)；Aspartate aminotransferase (AST) ≤3 x ULN ；Alanine aminotransferase (ALT) ≤3 x ULN ③Serum creatinine ≤ 1.5 x ULN, or calculated creatinine clearance (determined as per Cockcroft-Gault) ≥ 50 mL/min at screening ④INR, APTT, and PT≤ 1.5 x ULN ⑤Serum albumin≥ 28 g/L ⑥ECG showed no evident abnormality Written informed consent  Exclusion Criteria:  Known hypersensitivity or contraindication to any component of cetuximab or PD-1 monoclonal antibody or macromolecular protein reagent. A history of other malignancies with a disease-free survival of less than 5 years, with the following exceptions: adequately treated basal or squamous cell skin cancer, carcinoma in-situ of the cervix, and gastrointestinal tumors treated curatively with endoscopic mucosectomy; Any active autoimmune disease or a history of autoimmune disease Use of immunosuppressive medications or glucocorticoid therapy ≤2 weeks prior to entry Uncontrolled active infection requiring antibiotics Known history of HIV infection or active hepatitis  Severe complications, including any of the following:  ①Massive gastrointestinal bleeding, perforation, or gastrointestinal obstruction ②Symptomatic heart disease ③Uncontrolled diabetes and hypertension ④Uncontrolled diarrhea Women who are pregnant or lactating and people who do not agree to avoid pregnancy Patients with serious psychiatric that may interfere treatment. Other conditions which are inappropriate to participate in the study confirmed by investigators.