Inclusion Criteria:  Male or female, age ≥ 18 years old, ≤ 75 years old; Metastatic colorectal adenocarcinoma confirmed by histology, metastases cannot be removed; RAS gene mutation; ECOG performance status of 0-1; Life expectancy≥3 months;  Adequate organ and bone marrow functions:  Neutrophils >1.5×109/L, platelets >100×109/L, and hemoglobin >9 g/dL; Total bilirubin <1.5×upper limit of normal (ULN); aspartate aminotransferase (AST)/serum glutamic-oxaloacetic transaminase (SGOT) and/or alanine aminotransferase (ALT)/serum glutamic-pyruvic transaminase (SGPT) <2.5×ULN (<5×ULN in case of liver metastases); Creatinine clearance (calculated according to Cockcroft and Gault)  50 mL/min; Urinary protein / creatinine ratio < 1 (or urine analysis < 1 + or 24-hour urinary protein < 1g / 24 h); Women of childbearing age must be willing to use adequate contraception during study drug treatment; Informed consent has been signed; According to the definition of RECIST 1.1, tumor lesions are considered measurable if they demonstrate progression;  Exclusion Criteria:  Active autoimmune disease requiring systemic treatment occurred in the previous 2 years; Diagnosed as immunodeficiency or experimental treatment is receiving systemic steroid therapy or any other form of immunosuppressive therapy within 7 days prior to the first dose. After consultation with the sponsor, the use of a physiological dose of corticosteroids may be approved; Adverse events caused by anti-tumor monoclonal antibodies (mAbs) within 4 weeks prior to study day 1 or drugs received 4 weeks prior to the study have not recovered; Adverse events caused by chemotherapy, targeted small molecule therapy, or radiation therapy within 2 weeks prior to study day 1, or previously received drugs, have not recovered (ie, ≤1 or reached baseline levels); Female subjects who are pregnant or lactating, or who are expected to be pregnant during the planned trial period (from 120 days after screening visits to 120 days after the last dose of study treatment, or 180 days after the last dose of study treatment), or Male subjects whose spouse is pregnant; History of infection with human immunodeficiency virus (HIV) (HIV 1/2 antibody) is known; Active hepatitis B or C; Live vaccines were vaccinated within 30 days of the start date of the study treatment plan; RAS wild type.