Inclusion Criteria:
* 18\~85 years old.
* Histopathologically confirmed patient with an inoperable metastatic colorectal adenocarcinoma.
* pMMR or MSS.
* CR, PR, or SD (according to RECIST v1.1 criteria) achieved after 12-16 weeks of intensive treatment with a first-line chemotherapy regimen containing irinotecan/fluorouracil or a three-drug chemotherapy regimen containing oxaliplatin/irinotecan/fluorouracil plus bevacizumab.
* If previously received neoadjuvant or adjuvant therapy, the time interval between initiation of systemic first-line therapy and the date of last dosing must be at least 6 months.
* ECOG 0\~1, patients ≥75 years old need an ECOG score of 0.
* Normal bone marrow and organ function: ① Neutrophils (ANC) ≥1.5×10\^9/L, platelets (PLT) ≥75×10\^9/L, hemoglobin (Hb) ≥85g/L, albumin (ALB) ≥30 g/L, white blood cells (WBC) ≥3.0×10\^9/L, and no bleeding tendency; ② AST, ALT and alkaline phosphatase (ALP) were all ≤2.5× upper limit of normal range (ULN), and ≤5×ULN when liver metastases occurred; The total bilirubin level doesn't exceed the upper limit of the agency's normal range; Serum creatinine (Cr) ≤1.5×ULN or creatinine clearance ≥60 ml/min (calculated according to Cockroft-Gault).
* Understand the situation of this study, patients and/or legal representatives voluntarily agree to participate in this study and sign informed consent form.
Exclusion Criteria:
* Known or suspected central nervous system metastasis.
* Had received surgery or other treatment for tumors other than intensive treatment (including chemotherapy, radiotherapy, research treatment, etc., within 4 weeks prior to enrollment, if the interval between the current treatment was longer than 5 drug half-lives, could be included).
* Previous treatment-related toxicity did not return to NCI-CTCAE v5.0 I or below (except for alopecia, peripheral neuropathy).
* The use of CYP3A, CYP2C8, and UGT1A1 inhibitors or inducers couldn't be discontinued or were not discontinued within 2 weeks prior to enrollment.
* The presence of severe gastrointestinal dysfunction or gastrointestinal perforation, intraperitoneal abscess, and fistula.
* Intestinal obstruction, signs and symptoms of intestinal obstruction, or the stent has been previously implanted and the stent has not been removed before the screening period.
* Interstitial lung disease.
* Tendency of arterial embolism and massive bleeding within 6 months before enrollment (except surgical bleeding).
* Patients with fluid accumulation that couldn't reach a stable state but small amount of ascites on imaging without clinical symptoms could be enrolled.
* Any serious or uncontrolled systemic disease, including uncontrolled high blood pressure, heart disease, active bleeding, active viral infection, etc.
* Have had other malignancies within the past 5 years or currently, except cured cervical carcinoma in situ, uterine carcinoma in situ, and non-melanoma skin cancer.
* Patients of childbearing age who refuse to take contraceptives, women who are pregnant or breastfeeding.
* The researchers didn't consider it appropriate to participate in this study.
