The purpose of this study is to compare the effects and safety of Anlotinib with placebo in patients with metastatic colorectal cancer refractory to standard chemotherapies.

Anlotibib (AL3818) is a kind of innovative medicines approved by State Food and Drug Administration（SFDA:2011L00661） which was researched by Jiangsu Chia-tai Tianqing Pharmaceutical Co., Ltd.To compare the effects and safety of Anlotinib with placebo in patients with metastatic colorectal cancer refractory to standard chemotherapies.

Inclusion Criteria:

1. Signed and dated informed consent；
2. Histological or cytological documentation of adenocarcinoma of the colon or rectum；
3. Subjects with metastatic colorectal cancer (Stage IV),With measurable disease (using RECIST1.1)；
4. Progression during or within 3 months following the last administration of approved standard therapies which must include Fluorouracil or its derivatives, Oxaliplatin, Irinotecan；
5. ECOG PS:0-1,Life expectancy of more than 3 months；
6. main organs function is normal；
7. main organs function is normal；

Exclusion Criteria:

1. Prior treatment with Anlotinib；
2. Major surgical procedure, open biopsy, or significant traumatic injury within 28 days before start of study drug；
3. Known brain metastases；
4. patients with severe and failed to controlled diseases；
5. patients occurred venous thromboembolic events within 6 months；