The incidence of prerectal resection syndrome (LARS) after middle and low rectal cancer surgery is as high as 70%, which seriously affects the quality of life of patients. Studies have shown that colon pouch can reduce and alleviate LARS symptoms. However, most previous studies focused on open surgery, and the evaluation index lacked objectivity. Therefore, in the context of minimally invasive rectal cancer surgery, it is necessary to re-evaluate the value of improved surgical methods for the prevention of LARS, so as to improve the quality of life of patients.

The incidence of prerectal resection syndrome (LARS) after middle and low rectal cancer surgery is as high as 70%, which seriously affects the quality of life of patients. LARS may be related to the injury of anal internal sphincter, anal sensory nerve injury, defecation reflex pathway injury, changes in anorectal Angle and rectum sigmoid Angle, changes in new rectal sensory function and compliance, and changes in dynamics,etc. After AR surgery, the rectum loses its good compliance and the storage capacity is reduced, which is one of the important reasons for the increased frequency and urgency of defecation.Therefore, on the basis of traditional colon-rectum (or anal canal) end-to-end anastomosis, "J" shaped pouch anastomosis, end-to-end anastomosis, coloplasty and other special anastomosis methods were performed. Meanwhile, for the lack of objective evaluation index, the results were not credible. The LARS score was first published in 2012,and has been validated, evaluated, or used as an outcome measure in more than 30 published scientific papers. Further more,laparoscopic surgery is widely used in gastrointestinal surgery. Herein, current randomized controlled trial comparing coloplasty with straight colorectal anastomosis in LARS in order to guide clinical practise was conducted.

Inclusion Criteria:

• 20 years old ≤80 years old, regardless of gender, signed informed consent,
• BMI≤kg/m^2,
• Primary rectal lesions are pathologically diagnosed as rectal adenocarcinoma by endoscopic biopsy,
• The distance between the tumor and the anal margin is 5cm to 12cm,
• Preoperative tumor stage is T1-4N0-3M0,(according to AJCC-8th TNM tumor staging),
• Normal anorectal function and LARS score ≤20.

Exclusion Criteria:

• Patients with inflammatory bowel disease, chronic constipation, irritable bowel syndrome and other intestinal diseases that may affect bowel function,
• Patients with large tumors or extensive invasion of surrounding tissues and organs, TME is not applicable,
• Long-term use of drugs (such as morphine) that may affect bowel function,
• Patients with a history of abdominal, pelvic and anorectal surgery,
• Patients with severe mental illness or who cannot be evaluated due to cultural or psychological reasons.