The current clinical trials and data on the triplet regimen combined with bevacizumab for first-line treatment of metastatic colorectal cancer were from European and American populations. The triplet regimens recommended by the NCCN and ESMO guidelines using irinotecan and 5-FU at a higher dose intensity cause a high incidence of adverse events in Asian population, and there was no high-quality data on efficacy in Chinese population, both of which have limited the clinical applications of the regimens in China. This study intends to conduct an improved triplet regimen (mFOLFOXIRI) combined with bevacizumab versus mFOLFOX6 combined with bevacizumab as a first-line multicenter, randomized, controlled phase III clinical trial in patients with advanced colorectal cancer. Progression-free survival (PFS), observable response rate (ORR), overall survival (OS), disease control rate (DCR), surgical resection rate, and safety and health-related quality of life (HRQoL) were assessed in the two groups of subjects.

Inclusion Criteria:

- Histological or cytological documentation of adenocarcinoma of the colon or rectum. All other histological types are excluded.

Subjects with metastatic colorectal cancer(CRC) (Stage IV). Subjects treated with oxaliplatin in an adjuvant setting should have progressed during or within 12 months of completion of adjuvant therapy.

Subjects who have withdrawn from standard treatment due to unacceptable toxicity warranting discontinuation of treatment and precluding retreatment with the same agent prior to progression of disease will also be allowed into the study.

Metastatic CRC subjects must have measurable or non measurable disease according to Response Evaluation Criteria in Solid Tumors (RECIST) criteria, version 1.1.

Eastern Cooperative Oncology Group (ECOG) Performance Status of 0 or 1. Adequate bone marrow, liver and renal function as assessed by the laboratory required by protocol.

Exclusion Criteria:

- Previous or concurrent cancer that is distinct in primary site or histology from colon cancer within 5 years prior to randomization.

Significant cardiovascular disease including unstable angina or myocardial infarction within 6 months before initiating study treatment.

Heart failure grade III/IV (NYHA-classification). Unresolved toxicity higher than CTCAE v.4.0 Grade 1 attributed to any prior therapy/procedure.

Subjects with known allergy to the study drugs or to any of its excipients. Current or recent (within 4 weeks prior to starting study treatment) treatment of another investigational drug or participation in another investigational study.

Breast- feeding or pregnant women Lack of effective contraception.