Drugs used against cancer work in different ways to stop the growth of tumor cells, either by killing the cells or by stopping them from dividing. Monoclonal antibodies, such as CMAB009, can block tumor growth in different ways. Giving combination chemotherapy together with CMAB009 as first treatment after diagnosis of a metastatic colorectal cancer（first-line treatment）may improve the treatment efficacy. However, it is not yet known whether giving combination chemotherapy together with CMAB009 is more effective than combination chemotherapy alone. This open-label trial investigates the effectiveness of CMAB009 in combination with a standard and effective chemotherapy FOLFIRI（5-Fluorouracil /Folinic acid plus Irinotecan）for RAS/BRAF wild-type, metastatic colorectal cancer in first-line setting, compared to the same chemotherapy alone.