This study is to compare the short-term and long-term outcomes of traditional laparoscopy-assisted surgery and total laparoscopic surgery with no incision (natural orifice transluminal endoscopic surgery, NOSES) for colorectal cancer and to find a better surgical method for patients.

Inclusion Criteria:

1. All cases should be diagnosed as rectal or sigmoid colon cancer by histology or cytology. The tumor is 5-20cm from the pectinate line. The clinical stage is T1-2, N0, M0 for rectal cancer and T1-T3, N0-2, M0 for sigmoid colon cancer.
2. Eastern Cooperative Oncology Group (ECOG) scale 0-2
3. Heart, lung, liver, and kidney function can tolerate operation
4. Patients and their families are able to understand and be willing to participate in this clinical study and to sign informed consent.

Exclusion Criteria:

1. history of colorectal malignant disease
2. recent diagnosis of other malignant tumors (except for papillary carcinoma of the thyroid gland and basal cell carcinoma of the skin)
3. patients with intestinal obstruction, intestinal perforation, bleeding requiring emergency surgery
4. a history of abdominal surgery (which makes it difficult to perform laparoscopic procedures), severe systemic disease such as diabetes, severe chronic lung disease, cirrhosis, other malignant diseases
5. combined colorectal multiple carcinomas
6. poor anal function before operation and incontinence of defecation
7. with a history of serious mental illness
8. pregnant or lactating women
9. The researchers believe that the patients are unsuitable to participate in the researchers with other cases. A patient or family refusal to join

There is no plan to make individual participant data (IPD) available to other researchers.