The goal of this clinical trial is to learn whether early postoperative colonoscopy is valuable in the early diagnosis of anastomotic leakage after surgery for low colorectal cancer.The main questions it aims to answer are:

1. Will the median diagnosis time of AL in the intervention group (early colonoscopy group) be significantly shorter than that in the control group?
2. Can targeted treatment (such as endoscopic vacuum therapy (EVT)) be initiated earlier in the early colonoscopy group, thereby reducing the incidence of AL and the rate of unplanned re-laparotomy?

Researchers will compare the median diagnosis time of AL in the intervention group (early colonoscopy group) with the control group to observe whether early postoperative colonoscopy can detect anastomotic leakage earlier.

Participants will:

Experimental group (early colonoscopy group):

1. Colonoscopy will be performed on the 5th to 8th day after surgery (the surgeon will decide the specific date within this time window based on the patient's recovery).
2. Carry out adequate intestinal preparation before the examination (the specific plan is formulated according to the hospital's routine, which may involve antegrade or retrograde enema, etc., and needs to be recorded and standardized).

Control group (routine observation group):

1. Receive standard postoperative management, including monitoring vital signs, abdominal signs, drainage fluid properties, etc.
2. Only when clinical symptoms suspected of anastomotic leakage occur (such as persistent fever, worsening abdominal pain, turbid drainage fluid or stool samples), CT scan, gastrointestinal angiography or diagnostic colonoscopy should be performed according to clinical indications.

Inclusion Criteria:

1. Age 18-80 years old.
2. Pathologically diagnosed as colorectal adenocarcinoma.
3. The distance between the lower edge of the tumor and the anal verge is ≤15cm.
4. Accept laparoscopic or open radical resection and complete primary colorectal or colosal anastomosis.
5. Voluntarily participate and sign the written informed consent.

Exclusion Criteria:

1. Distant metastasis was confirmed by emergency operation, palliative operation or intraoperative metastasis (M1).
2. Unsatisfactory anastomosis or poor blood circulation were found during the operation, and reinforcement suture or preventive colostomy were performed during the operation.
3. There are serious contraindications for enteroscopy (such as acute myocardial infarction, severe cardiopulmonary insufficiency, blood coagulation dysfunction, etc.).
4. Pregnant or lactating women.
5. Previous history of colorectal surgery (except endoscopic polypectomy).
6. Unable to understand or cooperate with the research process.